Single stage yes, I agree, but I now use acrylic enamel because the urethane builds up too much in the fins and nooks and crannies.
You can use cheap, non high temp spray paint out of a can from the hardware store. However your petroleum vapors will eat it, as will outright fuel spills.
Some of the guys buy premixed single stage automotive paints and clears in aerosol cans- about 20 bucks a can.