Remember that your $ startup is just a portion of the cost. If you get a bigger tank, you're going to need to do bigger water changes, use more salt, and a lot more energy with pump, lights, powerheads, etc. So once you factor all those in, then you should start thinking about a tank size. It'll be fun setting everything up for that first month, but when you start getting utility bills in and they've gone up, you want to make sure you expect it and save accordingly.
Also if you're starting up a reef tank, make sure you don't plan on moving for the next couple years, just so you can get maximum enjoyment out of everything. A lot of the more popular and eye-appealing animals need tanks that have been established for over 8 months. If you're in a dorm/apt, start with FW
and then setup the reef tank when things get more permanent.
*Look for a tank that is more wide than tall (ie, bigger footprint). You'll regret it if you don't.