Rowan,
I purchased a excellent Next Gen over 2 yrs ago and paid $3500 cash 2 x days before xmas from a QLD seller. At that time, it was about $1500 off the going prices. There were not many around at the time, and it had been a difficult pin to find in excellent working condition.

Then, 6 months later, I paid $4,000 for a second nice Next Gen for my brother Rob. Again, prices at that time were around $4500 and had come down a little.
(since these times 2 yrs ago, I reckon over 100 containers of pinballs have been brought into Australia, and with it, probably a good hundred Next Gen Pinballs with those containers).

The prices at Xmas just gone, when the market was shithouse, were around the $2500 to $3000 foir a nice one.
I reckon prices have firmed up a bit since Xmas, and I reckon u will have to pay $3500 to $4,000 for a nice one.

Note- there seem to be none around at the moment, although ebay has new stuff coming n going all the time.