I think they are all selling in the $3 to $6 range from what I have seen. I think they are all selling in the $3 to $6 range from what I have seen.
Not to be too nitpicky, but this is a variety not an error. That said, you need to figure out the DDR number (and any cross-references) from either Billy Crawford's site (http://www.dvnmagazine.com/fyandecvarieties.html) or John Wexler's (http://doubleddie.com/). Then check eBay. Benjamin is probably correct that $3-6 is about the going rate, unless that is it happens to be a new variety or a recently discovered one - that's different - then $15-50 is possible (which is crazy), but there's a group of collectors that have to have it first and pay more. Yours looks familiar and I am sure you'll be able to find it. Let us know what you come up with. Good luck.
