Man, sorry to hear about that problem.
If you go over to www.dicor.com,
then click on Roofing, and then Installation Information it will give you a bit of an idea of what is involved in removing or installing an EDPM roof.
I'd guess there isn't much of a way to tell how much water damage there might be until the vents, trim, roofing and underlayment are removed.
Here where I live there is an independent RV repair shop that has a good reputation for quality repairs at reasonable rates, and they are also willing to give advice. Maybe there is something like that where you live? Any way you go, though, I'm afraid it isn't going to be cheap.
Welcome to the forum, and be sure to keep us posted.