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...
I agree with what you are saying. Yes they are overpriced and its hard to make any decent profit off them, even with free electricity. But there is still huge demand for S7 and thats why prices are still high.
The cheapest S7 I have ever saw sold was for $425USD a few weeks ago at 0.9BTC.