I'm curious too. Add farfalla and locomotive to the list too

It's not about cost, it's about finding them for sale in the first place...especially if you're in the US. Good luck finding Spooky...and there are a lot of people looking for one.

Time Machine would probably be the easiest to find in the US , Just a guess on price but somewhere in the range of $1,000 + or - depending on condition .
Pinball Champ my friend bought one a few years ago for $500 in decent condition but it was missing a lens insert in the playfield , Other wise nice .
Robot great game not so easy to find , around 7 years ago my friend got one for $1000 in nice condition , I would have no problem paying him $1600 for it today but he could probably get more and has no intention of selling it any time soon .
Farfalla could have bought one last year from a friend $1000 and it would have come with an extra (mostly populated ) playfield . I did buy just the playfield .
I bought a Devil riders from a friend not too long ago paid $200 but it needed quite a bit of work and had no backglass

would LOVE to get my hands on a magic castle one day... wishing wishing...