You have to budget for accessories as well as the bike: helmet, fenders, rack, lights, waterbottle, whatever you think you might need. It is easier to get discounded extras than discounted bike.
Find out what brands your local bike shop (LBS) does.
Fuji and Jamis are 2 brands where you pay less for the label.
http://www.fujibikes.com/2005/mtb.asp
http://www.jamisbikes.com/hardtails.html
most of the $4-500 weigh in at 30lbs, whist their flat-bar road bikes are closer to 24lbs.
Try picking up similar priced bikes and see how that feels.
Trek,Giant,Specialized are all big brand names and do similar models. First find your LBS.