I always wonder the same thing. I've been sitting on my Mermaid playfield for quite a while now, but mine is not for sale. Still hope to find a machine one day that doesn't need a mortgage to own.
I think the last one that sold went for $9,000 and the playfield was shot.I'm sure they would have paid $2500 for a new one, but of course I could be wrong. I attached a pic of the $9000 machine. I also know of a really nice original for sale now for $20,000.
And MB, I believe only 1 run was ever made. CPR made them with Clay

Shot Mermaid playfield (resized).jpg