Ken's got it right.
The books are worth whatever someone is willing to pay for them.
I just sold my Beatles "butcher block" cover to a former associate of mine.
I picked it up for $75 in 1976, and he bought it for $1500.
It was an "unpeeled" cover...the new cover had been pasted sloppily over the original cover...and you could see the old cover through the new one when you examined it.
He asked me "Will you be upset if I try to peel it?"
And then laughed when I replied "Hey, Steve, you bought it...I don't care if you put it in the bird cage."
I'm still regretting not buying the Gauntlet Press books I saw at the VNSA book sale yesterday.
"You have the right to remain silent. If you choose to waive this right, I may have to kill you in self-defense because you're boring me to death."