I would say the biggest factor in choosing your bike is... how much riding will you do outside of commuting to work? A 1 mile trip to work is easy no matter the bike, so if you use the bike only for commuting, an old used road bike or mountain bike in good mechanical condition will do. Price? I bought a good commuter bike for 5$ once in great condition! The commuter I have now cost me $50 Canadian, and is still running strong 1000+ km later. Check garage sales, friends' basements or garages, local classified ads, etc.
Another thing to consider is what you would want to put ON the bike. This can include:
- front and rear lights (required by law most places at night)
- water bottle cage(s)
- fenders
- bike lock (a must)
- helmet
- rear rack
And maybe other accessories you might find useful.
Good luck!