My home server is an ASUS NUC 14 Essential which idles at 5W with a bunch of services running. Its peak performance is probably less than the Mac Mini, but the hardware is cheap (at least it was before RAM/storage got expensive) and it’s a great platform to run Linux on.
It takes almost 8 years for $3.25/mo of electricity savings to break even with a $300 difference in up front cost. Assuming the time value of money is zero, that is.