You're right, the coupons have expired.  You're missing the point though.  A month ago these things were going for $450/unit from the manufacturer... The price has fallen out of the bottom with the halving in 45 days.  (I was picking up S7 with PSU bundles for $400 a month ago).

Just do a bit of quick math.  Assume modest 5% network growth per interval.  Take dirt cheap electric rates of $0.035/KwH.  You get a total net revenue of $320 from this unit before it runs in the red.  And that's after 300 days.  Between day 180 and 300 it makes a whopping $20.

So in 6 months you'll be in the hole $100/unit with the possibility of shorting that to $80/unit if you can wait another 4 months...

That's assuming you have free and available PSUs ready to go...