What are you wanting to do - go away from analog or use the equipment you already have? Is your Pro S surplus gear to you?
I bought a Pentax PZ-20 body to replace a P30t that was no longer working. I paid $17 for the bargain-grade body from KEH. Back when this camera was new it would have cost me several hundred dollars. I got it for next to nothing because they're not worth much. That didn't matter to me, I wanted a nice camera to use and didn't want to pay a lot for it. And I didn't.
If you want to keep using your Pro S, then do so and don't worry about how much it's worth.