go craigslist for a used bike, no problem with that and theres a chance you cold be buying a half way decent bike for dirt cheep.
I got a new bike from http://www.bikesdirect.com
Cant complain with my choice. I spent $400 on a halfway decent cyclocross bike (Gravity "Liberty CX"... which I think is a Giant knock-off) to get me to class in the snow and love it. Site looks a little sketch, but I assure you its legit. A lot of the bikes are off brand/knockoffs. Sometimes this means lower quality parts, but if your just commuting... who cares.