My suggestion would be to visit few shops in your area.
This way you can try lifting and riding some bikes to see
which one suits you best. Get one with a few gears; it
helps when you're bike is loaded and/or the wind is blowing
hard. You should be able to find a model well below your
budget. Use the left over for things like helmet, locks,
lights, fenders, etc. Good luck and let us know which
one you end up with.