He is worth as much as someone is willing to pay for him and what you are willing to sell him for, at any given moment.
I have a female Carpintis with a huge tube...I'd pay around $50 for a 6-7" Fader or RT (any grade)
However...someone desperate of selling will post for $80 and in 2 days accept $20 in the end.
It is what you're willing to get RID of, or what you willing to PROFIT from it.
It is what you NEED to have for your project , or what you're just WANTING to get.