I've got a Sea & Sea MX-5 which is a 35mm with a built-in flash. Buttermanr speaks the truth about the external strobe. If you get right up on something, the picture turns out OK (well, ok for an underwater newbie photographer like myself anyway, would probably get laughed off this board), but if you're any distance away, or the water is heavily silted, then you're just wasting film.
I got a real good deal on a Sea & Sea Seamaster Pro (which has external strobes), but haven't had a chance to use it (it cost me $500, so is out of the price range you mentioned).
Finally, I just purchased a C-5050Z digital camera. Don't have a housing yet, but I plan to get one at some point. The big benefit I see is that you don't have to pay for developing and printing of bad pictures. Currently, on a roll of 36 exp film, I wind up really only having one or two good pictures. With digital, this is no problem. This camera has two slots for memory - I've got a 512mb card in one slot, and the other can handle at least that much. With the 512mb card, I get somewhere between 200 and 300 pictures - way more than I could possibly take on a two-tank boat dive, and possibly more than on a whole dive trip. Of course, it was $529 for the camera, so also out of the range.
I guess my advice would be to buy the nicest camera (in terms of features, external strobes, etc.) that you can (even if you have to save up some more $$$ to get it), and try to get one that you can "add on" to. Even if you can't get the strobe right now, or the macro lens, get the camera, but be prepared for some disappointing pictures mixed in with the good ones. Then as time and $$$ permits, you can expand your system and get the performance you need. With the MX-5, there's really not anything you can add (other than a macro lens) - it doesn't support and external strobe. There's a newer version out that does, but I understand that the strobe is still fixed in place and direction, so you're still going to have the problems with silt. Don't remember what I paid for mine, but looks like the MX-5II is somewhere around $155 for the camera, and $160 for the strobe.
Here's a web page with pictures from the MX-5 (taken on one of our open water training dives, so no DIR comments, please!):
http://www.employees.org/~bjg/Diving/Dives/10-01-Kauai/10-01-Kauai.htm
You can see what people are talking about with the silty photos quite easily (i.e. a good example of a bad photograph!), but there are also some decent ones. If you look at the pictures from Nassau, those were taken around 95-100 fsw.
Another option (for the interim) would be to see if any dive shops where you're going rent cameras (of course, those are usually pretty low-end ones, and you probably don't have a lot of time to get to learn how to use it), but might be an avenue to explore. If not, you could always try to buddy up with someone who has a camera, sweet-talk them about how nice it is, and how good of photographs you bet it takes, and then hit them up for copies of their pictures.