If you have a local bicycle shop (LBS) that you have some confidence in, make sure you get the target bike checked out. Ultimately, what really matters is that it's a bike you *will* ride ... personally, I'd go with an old Gary Fisher (I've got one from the early 2000's that still is solid and quite ridable).
w.r.t. budget, make sure you budget for good lights, a bag (pannier, backpack, whatever works best for you).
You don't mention anything about your commute (distance, hills, weather, plan to ride all year...) so extra hard to guess what might work well for you.
Oops, that definitely is important! My daily commute to school would be only about 2 miles each way and flat. I am located in Wisconsin, so I don't know that I want to deal with trying to bike through snow and ice -- weather shouldn't be much of an issue. I do live in a pretty hilly area, so I am not really interested in cruiser or one speed bikes. Is that enough info?
Again, thanks so much for the input.