I can't claim a poster that fits the category, but back in 1990 I got a Frazetta painting for $6000 (I got it from Russ Cochran, of West Plains MO.)
it was the Uncle Creepy portrait that was used for a print you could buy through the Captain Company ads in Creepy, Eerie, Famous Monsters etc.
I got it home, put it on my wall. A friend came over, saw it and made me an offer. Made me a higher offer. Made me a higher offer. but I did not sell it
his next time in town (I was living in Cincinnati at the time with my ex-wife) he came over and made me a higher offer and then he finally offered me $17,500 and I just couldn't say no anymore. I had the painting for less than 6 months