I'm newly returned to cycling. I liked Trek back in the day, so I decided to go with them again. For what it's worth, I'm one year older and one inch shorter than you. I went with the Trek DS 8.3 and it was close to your price range. Has front suspension which can be locked out when you're on the road. I think it would now be just DS 3, and you may need to go to a DS 2 or DS 1 to get in the $500s, but they're good bikes. I've had it a year, put some good miles (road and trail) and really liked it. Just something else to consider that your LBS may have in stock.

EDIT: And I went with the 21 size frame.