Welcome! I started a little over your weight, and put close to 1,000 miles on a late 90's low-end Raleigh MTB before buying a new bike. Worked fine for me, what finally made me buy a new bike was a chaos of repairs - new tires, new chain, then two popped spokes in one day. I picked up a '07 Hardrock Sport when I was still over 400, and it's got about 2,500-3,000 miles on it, been great for me and I paid $349 for it new.
Now I'm down to 340, and I still love it - two years later. Granted it's had it's share of abuse related issues, just discovered yesterday that the rim is cracked around some of the spoke holes - I don't blame it too much, though. I mean seirously, $350 and I've ridden the thing like I stole it every time I've gotten on it, and it's only once left me stranded. Can't say that about my other bikes
. I'd recommend one, just swap the tires with some Specialized Nimbus slicks and you're good.
As far as fit, you'll need AT LEAST a 21in frame, maybe even one of the 23's. I ride a 19, and at 6 2 it's almost too small for me.
The Sedonas are extremely popular around here - both locally and on bikeforms - as are the Trek 7x00 series. All are excellent choices and will serve you well. In your price range there are definitely options.
Good luck!