I use the prices as a guide.
If you are buying from a dealer with a warranty, expect to pay more.
It really comes down to what you want to pay.
If the seller won't come down in price, you can walk and hope you find another one in similar condition for a lower price. If it's in really good condition and you really want it, go for it.
Only you can really decide what it's worth to you.
I looked a the same machine with the same amount of work done to it and seller was asking about $3500. I walked. If he was asking $2500 I probably would of walked also.
For $2500 for that machine, I would expect a perfect pf and no cracked plastics with almost a perfect cabinet.