I showed my Mantle to a guy years ago (20 at least) at a local card show and he said maybe around $1500-$2000 CDN if I was lucky?
Seeing and asking about it's current value, even with the front bottom damage, I have been told likely around $10,000 to $15,000 U.S.
Personally, I never would have sold it back then anyways but today I'm sure glad I didn't need to.
