"how is that exactly"
A few hundred bucks a year for a big company is pocket change. For a
small home, costs like these are more of a factor.
Also some countries have higher energy costs than others, which would only increase how important a factor it is.
With your proposed price difference of "$200" you'd make up that difference in savings in the first two years and end up with a device that is more or as powerful as the x86 option but more efficient.
Then it would all be savings going forward.
Whereas you could buy the cheaper intel nuc box, end up paying the $200 in power usage anyways, and still be paying more for power after the initial two years for a arguably worse product.
https://www.overclockers.com/how-much-does-it-cost-to-run-your-pc/