Around here a PMI runs about $150. Then a roof re-seal runs you about $500 (labor/material). I had both done when we bought our RV. I watched some of the work being done and when I reviewed the final work order, I was not impressed. There were things I discovered later that I felt should have been caught like leaky water fittings in multiple spots, failed voltage regulator in engine bay and loose terminals on the water heater solenoid valve. The PMI really is nothing you can't handle by just carefully looking at the whole rig. I also saw the end result of the roof re-seal. Again, not worth the money I spent. The metal roof is basically solid, so all they did was re-goop the edges and fittings on the roof with very little removal of old lap sealant. However, if you are looking to sell, I agree it would help to have a shop receipt that says you had the work done.
Jose