If it's saving you $2000, then it would have to be about free, or better. I'm using Valspar Wattyl Colourthane Polyurethane. So far I've painted the interior and a few small pieces with it and it holds up really well. Because it is an industrial paint (they use it for painting boats, bulldozers and tractors here) it is sold in large volumes and is thus way cheaper than other options, but can still be applied just as lightly as any other paint if desired. The total cost of paint for two coats of polyurethane on the exterior of my RV-7 will be $300. I'm sure Valspar sells the same paint under some other name in the US.
Tom.