Back of the envelope thoughts: Donating money is unlikely to be more efficient.

They have to be electron-juice too, and while it might be cheaper for them to buy it, they also have to pay for hardware on top of it.

Option A) You spend $10 on electricity and give them X MIPS.

Option B) You give them $15, they spend $5 on electricity, and then they have $10 to spend on hardware. I bet that they'd get far less than X MIPS!