I would strongly recommend you at least visit one or two local bike shops. The real issue with buying bikes from a department store is not the bike itself (since you can find "name brands" there now sometimes), but the quality of the build. Bikes need to be put together, and what I've seen at dept stores is downright scary. A real bike store might be $50 more, but that gets you a certain guarantee that they know how to put together a bike well, and that they will stand behind that bike and address any problems you may have.

I'll be that you may well find a suitable bike in your price range, and that the bike shop will give you good advice as to the most suitable bike for your purpose.