You need a bike for basic transportation, which is not a mountain bike. The people advising you are not bicycling experts!

I suggest a Jamis Commuter 3, which is in your price range, or a Breezer Uptown 8, or a Trek Soho, which might be above it. Specialized has some similar models, too--Globe Vienna looks ok. Need to add fenders.

You'll utilzed the rack and come to appreciate the fenders, chainguard, lights, and kickstand, none of which come with the purchase of a mountain bike.