Aluminum heatsinks are cheaper than you think. Probably about $5 worth of metal.
Find me those heatsinks for $5 with a MOQ of 2.
All those savings you listed are probably less than $50 and $25 to ship.
So you're just talking out of your ass then? May I take a moment to repeat what I said...
Why does the actual cost of the saved components have to actually be $300? They're valued at whatever BITMAIN decides to value them at and the rest of us just have to deal.
What exactly will you be doing with the old boards? Will you be throwing them away? That's ~$150 down the drain.
Sell them for 25$ and let someone else worry about it. Hell, if I'm so inclined maybe I'll have some of their control boards made up and sell those too.