I also think you should buy used. Craigslist has some awesome deals, but if you do not know what you are looking for, find a friend who does or stay away. I recommend seeing if any local bike shops have used bikes. This gives you someplace to bring it back when it breaks, and a place to get the helmet and lock you will also need.

Regardless of how safe your campus feels, buy a good lock. I ride to school every day, and park my bike 50 feet from the building I spend 95% of my time in. I feel safe on campus, and have neither heard of nor experienced crime there. I see multi-thousand titanium and carbon bikes with varied locks on them. One guy routinely "locks" his $800 mountain bike up by looping the cable lock he keeps on the rack around the handlebars. Seriously. The campus police tell me bicycle theft is the second most prevalent crime on campus, after laptops.

At a minimum, buy a U-lock and a cable-lock. Take the U-lock with you during the day when people will be around. When locked overnight, use both, with the cable lock securing both wheels if able, or minimally the other wheel and the frame.