It typically runs 120W idling, and 450W peak. Not great power efficiency wise, but I have a Cron midnight shutdown and and S5 bios event powering it up on a morning (I could use wake on Lan but didn't see the point).

(650/1000)(24*30)=468 kWh.

That would cost me about $70/month ($0.15/kWh) or someone in California about $234/month ($0.50/kWh).

Do you pay $1/kWh and make ~$1500/month or something? I can’t make the math work for your case.