I just replaced the floor in two of my slides bedroom and the large dinette, sofa slide. Both had water damage at the ends not in the center that area was solid. This was my first RV so I was not looking for this problem though I discovered it not long after purchase and my original thought was that it was minimal. Over the last 5 years it got to the point where I knew I would have to replace the floors and thought I was going to sit down at the kitchen table and wind up on the pad. On our way to Alaska last spring I stopped at Lowes and bought a 3/4 sheet of plywood to keep that from happening. When we returned from Ak I began the replacement. It turned out the plastic wrap was all that kept me from going through.
The cost of materials for the two slides were about $500.00 Marine plywood, waterproof epoxy paint and fasteners. I preformed the work at a friends place with a full shop of necessary tools though I performed all the work till we wrestled in the new floors which with a couple hands only took about 10 minutes.
The removal of the old floor was more work and took more time than installing the new.