Car rental in Mae Sot?

[dluek]

Heading up to Mae Sot on Tuesday and looking to rent a car and drive down to Umphang for a few days. Once there we'll probably arrange a private trip to Thi Lor Su Waterfall, so we don't need a SUV, just a car with enough power to handle the mountain passes along the sky road.

It appears that Thai Rent a Car at Mae Sot Airport is all out of cars on Tuesday. Avis shows cars available when searching through the main website, but when I go to the Thailand-specific Avis site it doesn't list Mae Sot as an option for picking up a car. All of the travel guides I've seen mention only Thai Rent a Car.

So I'm really hoping to find a small, privately owned car rental shop in Mae Sot. I'm guessing that I'll find one after arriving and asking around in town, but we're looking to land, pick up a car and head south as quickly as possible. Any help appreciated.