I'm not sure of the cash value of a tempest mini, but I know I would like one.
I know you are looking for complete machines, (that I don't have), but here is a crazy trade offer, maybe this will be too good to refuse.
some stuff I wasn't planning on selling, but for a tempest, I will.
48-1 cocktail, needs glass taito/nichubichu style
megatouch IV works great
19" g07 monitor no burn, still has nice picture without being recapped
sanyo 20ez no burn, recapped, except for the audio board,
crystal castles pcb, purchased as working from reputable KLOVer, never used by me.
crazy climber pcb with jamma adapter (there are not many games I would give this up for)
bad dudes vs dragonninja pcb
dragonballZ 2 super battle pcb
time soldiers pcb
Soldering practice boards. has caps, chips and all kinds of things to solder and unsolder, also plays big event golf
the wife would love this trade, not because of tempest, but because there would be a lot less stuff in the basement.