I'm still having some trouble understanding why people would do this. The owner is offering for you to bring your machine into HIS establishment, leave it unattended, and like you said, have it run 10-12 hours with possibly power surges sent to it etc etc, and all you get out of this is, whatever ends up in the COIN BOX?? You have totally just made his life a piece of cake.
I would have asked for at least $100 from him plus whatever lands in the basket (which could potentially end up being like 5 bucks). And I feel like that's still an underestimation. But hey, that's just me.