I’d say an actually NM/M copy would go for ~$30 on eBay.
Also, I don’t like being that guy, but searching the eBay sold listings would give you the best answers. Anyone who responds here would just be doing that for you and posting here.
+1 You have to look at it as how much you could conceivably sell it for. Furthermore, your example is not supportive of your case. Charizard 11/108 goes for $10-$11 on eBay, $10.50 on TnT, $9.50 on TCGPlayer, and $9 on Amazon (almost out of stock). That is, at max, a $2 disparity. With all of that said, it seems like you’ve taken the time to look at all of these different sites so what magical info could someone here provide about a card that would change the supposed value of it? I’m not trying to be flippant