My total electric bill per month Winter is $55. Summer (like August) is $90.
Of that, about $30 is my electronics left on 24/7/365.
Summer i am certain at least $15 of the added air conditioning is due to heat from my equipment.
So Summer: $45. Winter $30
(my heat is 'free' so it does not matter to the apt owners that my electronics heat up half the need for heat except Dec/Jan/Feb where the heat is really on all the time.
I can see big class A amps being left on 24/7 could add a hundred to a monthly bill.