I did some searching on the board, but couldn't find a price tag, just what it does and is needed for, so I hope making a thread is ok.
Also couldn't find anything on eBay or Amazon.
I found this today at a flea market. It also had a Mario game with it, but I don't know anything about Famicom games, so I'm not sure which one it is.
I'm guessing it's one of those pirated versions of a Mario game.
Since I don't have a NES right now I can't try it out and might just sell it.
Also, I found it on a flea market here in Europe, so I'm not sure if this is some kind of PAL version (but I guess not).