Can anyone tell me what a nice condition Spanish copy of this is worth?

Cheers

the best way to check value is to go onto ebay and search for the item in the case type: donkey Kong Jr Math NES  after you hit enter look down the left side and there will be a completed listings option.  Click that and change the search to lowest price plus shipping.  Unfortunately in this constantly changing market of nes games this will be your best option to find true value/what people will pay for it