Many/most RV parks in Florida that allow park models require a professional set up, doing a permanent connection to the sewer, water and electrical connections. Plus they require all park models to be skirted. I suspect to have a park model delivered to a park by the dealer and set up, you could be looking at $1,000 to $1,500 each time. Then to move it would be about the same. Many park models are wide enough to require a permit to move them on public roads, not something most of us would want to try with our pickups.
My wife and I considered buying a park model when we were full timing in our Class A motor home. Went up to Ocala, FL where several factories build them. But we ended up buying a double wide, in Homosassa FL, already set up in a park for the same money and got more room, an extra bedroom, etc.
Mobility, to me would be the main difference to me in a fifth wheel over a park model. More room, full sized appliances and bath room, would be the strong point of a park model. A fifth wheel allows you to move if you get hit with a large increase in lot rent, to a different campground, in a park model, you basically just have to grin and pay the increase.