This is a long shot, but try cracking the gas cap loose and see if it'll start. My mower, the gas cap gasket rotted away and the cap was sealing tight to the tank neck, and the tank wasn't venting. It would run fine until the tank vacuum-locked and the gas stopped flowing.
But that didn't affect starting, it started and ran fine. And would keep running if the cap was cracked loose, or the tank was 1/2 empty. The cap gaskets are designed to keep the gas in but still allow airflow for venting.
Go with an independent that's been mentioned, avoid the high-dollar shops. Mowers are just too damn simple to pay big bucks for repairs on. I guarantee it'll be a simple fix.