If you do it yourself, you'll save about $100/hr in labor rates. It's probably going to take a minimum of 10-15 hours for the shop to do it. The cost of the new membrane will be $1,000+. From the sounds of it, there will need to be some wood structure removal and replacing too. That's the cheap part though!
All in all, I'd guess you are looking at $3,000+ to have it done.
If you want to do it yourself, you can probably get it done for half of that. Whatever you do, make sure it gets done right.
2000 Jayco Eagle 313H - 32' Class C