I was looking for previous sales and I found this post [ https://bitcointalk.org/index.php?topic=214589.0 ]  that has a table. The multiplier there is 2.33 for an ANACS MS-65 brass error coin.  However,  that was before bitcoin cash which at face value should be good for at least .1 based on today's prices.

I would rather just hold on to the error coin for 1.6BTC.    However, I have a non-error coin MS-65 I would sell for 1.6BTC.

I suppose that 2.5BTC would be the minimum bid that I would consider selling it for.