[wayner]

My opinion doesn't mean much, but in general I always thought used parts were worth 1/2 of new on usual parts purchases (unless rare or special).

For higher end units like 911 performance motors, that might not always work, you could compare this to new car depreciation at a certain percentage per year or per miles.

I don't know the formula, but used is always worth less than new due to risk. Why would I pay close to new if I could buy new.

...now, 10k for a 20k motor is an interesting question. A reputable builder, a known installer, evidence of good health all add to the value of used for this sort of thing.

It seems most people would charge $1k to haul away a $10k motormeister engine, while a factory rebuild might go for close to the cost if well documented in all ways.