I would examine an entry level Fuji, Felt or Trek.

You can probably get in on a Fuji Roubiax or Trek 1200/1500 for around that price this time of year on closeout/clearance.

I would go for the best component spec you can buy and not worry about upgrading a bike in this price point (per comments above). Truth be told, I'm not sure many frames in this price point are worth the expense you would incur to upgrade by buying parts after market unless you are very selective. A full ultegra upgrad will run you $800-$1,000. Often you're better off selling the old and buying a full new ride than trying to upgrade components in this price range...but that's just my opinion.