I spent $1700 getting my Onan 4K repaired by Cummins a few years ago. The price is absurd, but even in a reasonably populated area I could not find someone who would even look at it. It has some major issues and Cummins made it work perfectly. It starts and runs every time in any weather. It's also very quiet and built into the RV. I can get one just as quiet to run outside, but a good one is expensive as well.
In the end some things just need to be done right and not skimped on. After driving through Arizona in July without AC, my wife made me see the light.