You will not know for sure until you cut into the floor. The membrane is not a good sign.
My current unit is only 1/2" OSB.
I can clearly see the OSB exposed under it.
I wish they had used a bit more like 5/8". That extra bit makes a big difference in plywood. Oh well. Such are the ways with Forest River.
Typical cost is all over the place. It is not a big job to do to patch it. Again, the problem is it is gonna look like a patch job.