How much should I sell my motorcycle with a blown engine for?

I have a 2004 Honda shadow spirit 750 with a blown motor. I don't know exactly what's wrong with it, i just know that there's zero compression in one cylinder and almost zero in the other. It has been sitting in a barn for 3 years and is pretty dirty. I'm going to sell it for parts and was wondering what a reasonable price would be. I was thinking $500, but I don't really know anything about motors or mechanics so any input would be appreciated.

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