I have been looking into heaters over the last couple of years, but have not jumped in yet. One that I found on ebay that seemed like a pretty good price was manufactured by Dornback Mfg. They are supposed to be made in the US in OH. Price seems pretty competitive:
GARAGE FURNACE GAS UNIT HEATER 45,000 BTU HEATERS NEW | eBay
Dornback Manufacturing
I've been holding off because I need to run a gas line to a detached garage. When I do buy one, I'll be getting one of these.