Fish in a dorm is one of the best decisions I ever made. They add so much, and really demand so little. I spend less than an hour a week on my tank [even though I religiously do water changes and vacuum] and it really adds so much.
My $0.02 is to go for a 10, 12, or 15 gallon. I know lots of dorms have limits on tank size, but a 10-15 gallon won't raise any eyebrows [my dorm has a 10 gallon limit]. A 10+ gallon tank will allow you a lot more variety in fish, and more breathing room when it comes to tank maintenance. With a 3-5 gallon, there's a lot less volume, so ammonia/nitrates/nitrites can build up rather quick-- and a water change can GREATLY alter water chemistry and hurt your tank.
It's MUCH easier to maintain a larger tank. It'll save you time, frustration, and give your fish more room. It will probably be the same price in the end. It may not appear this way, but anyone on this forum will back me up on this point- it really is easier to go with a larger tank. Whatever you decide on, I hope you enjoy it as much as I enjoy mine.
Fishwise, I'd go with one gourami, some tetras or small livebearers, and a snail and ghost crabs. Gouramis are tons of fun to watch, tetras and livebearers are classics to the hobby, and ghost crabs and a snail will help you keep the tank clean and will add some variety.
~$100 setup (I know, $100 is a lot for a college student, but this setup will last for quite a while...)
$30 for a 10-15 gallon tank with hood and filter... $4 for gravel, $15 for decorations, $10 for a couple plants, $8 for some food, $10 for a heater.
then $23 left for your fish- that should be PLENTY.