It sounds like a used road bike will suit you well. I was in your position when I started college - I was used to mountain bikes and hybrids, but needed something practical for commuting over roads. I was amazed at how much easier riding was with a proper road bike. I would go to the used bike shop and see what they have to offer. You shouldn't have to spend more than 200-300 on the bike to get something decent or better. Try some different bar styles to see if you like riding upright all the time, or if you want something with drop bars. If you're looking to get by a bit more cheaply, you might want to try a single speed bike, which will also make maintenance much easier. If you want fenders/bags, be sure that the frame can accept them without too much trouble. Don't be afraid to thoroughly test ride it and ask the bike shop person if they have any recommendations for you. Also don't forget to budget for lights, lock, and helmet if you don't already have them. Good luck!