A good place to check for going prices is Ebay...you can search for completed items and see what the last couple have sold for. I did a quick look, and a 60 GB one sold for almost 700 and a couple of 10GB and 20GB ones sold for around 500. Most of those were never used items in the original box, so you should take that into account and drop your price expectations accordingly.
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Ninti - MK IIa 60GB Smoke, 30GB, 10GB