How much a dealer will charge for winterize a Pop-up?

I just did mine. Low point drains opened blew it out with air at 40 psi. Let it set for an hour and repeated. No waste holding tanks on mine so no P-traps. All I have left is the cassette toilet. Make sure fresh water tank and water heater are drained before blowing out. Years ago I had an attachment that would fit a vacuum cleaner to blow one out, it came with a pup we had back in the 70's. I don't know if they are still available.