Same size - Same budget . . . Except I've picked up three over the past year (see profile box to the left.)
Each one from my local Craig's List and $400 or less (not counting after purchase extras - upgraded saddles, lights, etc.)
I've lost 35 lbs. since 9 months just by biking and trying to eat 'better' overall, but not necessarily on a special diet.
Just get a decent bike and start riding . . . Good Luck!