1) I know you run a little side business refurbing these ECU's and I commend you on the fact that your work provides a functioning memory.
2) There are a couple of people selling the very same ECU I have here, on sites like eBay for well over $400 a piece with a $50 core charge.
3) Realistically, this part is worth somewhere between the price you charge (is it $300 plus a core) and your offer of $50 for a core.
You say you're not paying retail for the part but it seems you want me to, for all practical purposes, give the part away. I bet there are a fair number of late model Classic owners who would be more than happy to save some money and buy a part like this so they have functionality restored to their driver's seat.