For a 30 foot RV,
this one costs around $4000+. I had an appointment to have it done but had to get a new refrigerator instead so put it off for a while. This is a different product and procedure, but somewhat similar to the one you are investigating. I suspect that one would be in the #3000+ range for a 30 foot RV.
I think the one I linked takes all the roof equipment off and replaces all the vents, refrigerator vent, etc. with new. They also remove the air conditioner to do the roof. The end result seems to be about the same however.
Barney