My running a Forte 4a amplifier (stereo 50 watts/channel, high bias to class A, added $8 a month on my electric bill back in the 1990's
I leave all my stereo on 24/7/365 now, and my bill is about $65/mo without any air conditioning in my 1 bedroom apartment. (air left at 79F adds from $10 June, September, to $20 a month July August.)
Going from compact fluorescent to LED dropped my bill about $10 a month in 2016.
A lot depends on the idle wattage used. (how much the bias is toward class A)
Plus the heat generated has to be cleared by the air conditioning in Summer.
If it seems too much, one way to find a compromise is to turn it on the night before listening, and leave it off if not listening for several days.
I am retired and listen every day for many hours. So 100% on is my plan.