+1 to everything yank said.

It is really hard to offer any specific suggestions on here based on what you have told us so far. It is not for lack of information but more for lack of you own experience. That absolute best thing for you to do is go to a local bike shop and talk to them and test ride a few different styles. There will be plenty of options for you in your price range that will be wonderful rides.

Seeing that you are a student and therefore presumably rather young (early 20's). In todays world there is a strong inclination to shop and buy online for the best deals. However, buying from a local shop is without a doubt the best thing to do for cycles unless you are very VERY experienced. Fitting is massively important and online shops cannot do that. Plus, any changes or upgrades you want to make over the years will be much easier when you have a local shop you do business with. So I am saying it is worth the extra couple of bucks to go local - especially for your first ride.