I would say that most of this money would be spent on accommodation rather than the travel itself. In the Muggle world, flights are relatively inexpensive, while even modest holiday accommodation can cost hundreds of dollars a night. I don't think that travel would be entirely free of cost for wizards, though. Apparition and side-along Apparition would not be appropriate as it "...becomes increasingly unreliable over very long distances, and only highly skilled wizards are wise to attempt it across continents" (Quidditch Through the Ages, p.48). Brooms would also be inappropriate for obvious reasons, and I am inclined to think that the Floo Network is not international due to it being controlled by the British Ministry of Magic. Perhaps there is a Ministry-Approved wizarding travel agent that would set up a Portkey for a cost, or maybe there is an international service akin to the Knight Bus. Both options would likely cost a fair amount to transport all of the Weasleys. As to what guidelines there would be for wizards travelling internationally, I think they would reflect the Muggle guidelines in each country, as this is often dependant on the culture and attitudes of a nation, something that is largely shared by wizards and Muggles.

I think a lot of money would go to traveling from the UK to Egypt as the travel is inter-continental. And things like visa's may have to be made available for using Portkeys for international travel (which would cost a lot for the Weaslys who are really poor) But some of the money would go in staying there too.
I also think that some of the money would have been used for buying things like tickets for the various tourist places(wizarding) in Egypt. And on the international guidelines I agree with JNA.

There's a bit more involved with travel than you might think. There is accommodations to worry about, first and foremost. That alone, for even a small place - with a family like the Weasleys, you figure they would have to buy at least two or three rooms, or some sort of package. Then there's meals - again, this is a vacation for everyone, so I highly doubt Mrs. Weasley would be putting even her lovely cooking skills to work. Even with magical travel, It has always been my impression that, just like in the muggle world, they would have set up some sorts of customs offices, that stops wizards and witches from just travelling willy nilly. The Ministry tries to carefully regulate everything, and we learn in later books that Individual countries have ministries as well. I've always imagined that there's some sort of magical border crossing, where you have to go through checkpoints, make sure you're not, say, smuggling flying carpets back into the country - that costs money to go through as well.

And, of course, as every traveller and Harry Potter fan would know...there's also the fact that anything you buy in touristy places charge you an arm and a leg. So with the added cost of souvenirs, well...they could even go through more than 700 galleons on a week's vacation.

I don’t believe that the Weasley’s Apperated to Egypt because Ron seems quite impressed that Harry did Side-Along Apperation when he was with Dumbledore visiting Slughorn. Apperation seems to get harder the farther away you Apperate, which leads me to believe that it is only usefully for relatively short distances (within Britain, for example). I bet that the Weasley’s or any other magical family who is traveling internationally would go through the Ministry to get a Portkey. As for visa’s, I guess the bigger question is if the magical community is recognized by the British government. If you are a Muggle Brit and plan to travel to Egypt, you would need to get a passport and a visa through the government which would recognize you as a citizen. Are wizards legally citizens? I can only really speak for the United States, in which, upon your birth, you get a Social Security number. From then on, you report to the government every year to file taxes. Does the same go for wizards? Do they get a formal birth certificate from the government? Or is there another legal system through the Ministry of Magic that tracks the population? I know that this goes a bit off topic, but I always wondered how Harry fits into this. I assume that the Dursley’s had to have some type of legal form for him or else he would not be able to register for Muggle school. Did the Muggle British government every wonder why Harry (from their perspective) drop off the face of the Earth once he turned 11? Long story short, if the Weasley’s were never registered as official British citizens, they wouldn’t have been able to get a Muggle passport unless there are some wizards manipulating the system behind the scenes. I sure hope that the Egyptian wizard government knew that they were visiting.

We also have to remember that there may be wizarding exchange rates; we don't know that they use Galleons, Sickles, and Knuts in Egypt. I also think Ron might be exagerrating; would Molly and Arthur really tell their kids how much money everything was costing? Perhaps Ron just assumed most of the money was used on the trip, and then some of the rest on his wand. (which by the way, can we talk about Ron's new wand using the info on Pottermore when we get to that chapter? I think we could really analyze Ron's character through it.)

I was confused on how the Weasleys actually got there in the first place and I began thinking about all the ways wizards travel, and how it would cost money.
Apparition: Maybe there is an allotted amount of Apparition allowed before a certain price must be paid, and over long distances the price goes up.
Floo Powder: I fancy an idea that there are toll fireplaces in which wizards automatically drop when passing.
Portkey: I think this is most likely what the Weasleys used, although, I cant find a reason to pay for it.
After that, the list goes on, but I feel as though lodging near landmarks must have been extremely expensive. Actually a Muggle trip to Egypt would cost much more. And with souveniers and money saved and left over, the trip didn't come as cheap as we think.

I'm inclined to agree with everyone talking about taking a Portkey to Egypt. I think there would be some sort of licensing fee to set one up, though, because Fudge makes a really big deal about the fact that Dumbledore set up an illegal Portkey to send the Weasleys and Harry to Grimmauld Place when Arthur is injured in book 5. So, to get a Portkey to Egypt, the Weasleys probably had to go through an agency or pay money to the Ministry.
I always assumed they just stayed with Bill. However, I do like Caleb's idea that Molly and Arthur kind of went all out on the vacation because they don't get to do things like this very often.
I would guess that a lot of money also went on food, because though Bill probably has a kitchen, I assume the Weasleys would want to try some local food.
And finally, tickets to attractions would, I think, be the biggest cost. Ron definitely talks about guides taking them through the pyramids, which suggests some sort of organized company that runs a tour system.
Or maybe the Weasleys just went on a package tour--and they had to pay a per-person fee that included travel, accommodation, food, some tickets etc. Though I think this is a little unlikely because they do have Bill who probably knows all the good places to go and has connections.

I think most about where the galleons went has already been said so there's not much for me to add, but regarding SocksForDobby's mention of Voldemort and Wormtail traveling abroad; I sincerely doubt that wizards operating in secret would go through the trouble of complying with procedures. That'd defeat their entire purpose; to not be seen or caught. I do think there would be repercussions if a Ministry of whatever country would uncover a wizard travelling illegally, but then again, there are many magical means to conceal yourself. But as I don't doubt the Weasleys' willingness to operate within the law, I think it's very likely that they had travel and visa costs from their own Ministry for Magic and from that of Egypt.

RoseLumos wrote something about how Harry disappeared off the map for the British government when turning 11- I always assumed the answer was pretty easy. Ministry officials ensure that the records are wiped clean for Muggleborns who agree to enter Hogwarts School. If this didn't happen, parents of Muggleborns would get inquiries as to why they are denying their children education since they aren't registered at any school. So I think it's safe to assume that happens. :)

I think the Weasley's traveled by portkey ( as others have suggested) to go to Egypt. If travel in the wizarding world is similar to travel in the muggle world, there would be customs to go to and certain portkey points ( similar to airports) to go through and arrive at. Also they are probably costly if it is international. Once there the Weasleys would need a place to stay ( If they didn't stay with Bill ) and would probably spend money on tourist attractions and souviners and such. I believe the Weasley's spent most of the summer there as well so that would extend the cost of the trip. Ron could have exagerated the amount spent as well so it makes sense that they could have spent a large portion of the winnings on the trip to Egypt.