You can get a Kill-a-watt and see how much energy your equipment draws. It may be illuminating. As for the cost of leaving equipment on, you can compute the draw from your rate schedule, usually published in your utility bill. 60W x 24 hours x 30 days = 43200 watt/hours or 43.2 kW/hours. Here in southern California, the summer rate at worst case (301%+ of baseline) adds up to about 42 cents per kW/h. That is over $18. My Gryphon amps used to draw 500W each at idle; my Lamms drew 300 x 2. My bill was scary plus I was probably using up a lot of water (if a coal plant) which is bad news as we have a water problem as it is.
I have no idea what my carbon footprint is but I imagine it is not good, which is why I try to keep things off, use energy saving light bulbs, turn off lights in rooms I am not in (which is what I learned as a kid).
I have even tried LED bulbs - they work okay but now that two have died before 100,000 hours (or since I have 5, stochastically, 20,000 hours, which is not, however 4 months) at $30 a pop, they are a no go.
All of which is to say that stereo gear can easily cost $50/month or more just on idle. The Lamm pair of amps alone would cost $180 to leave on all day (600W constant).
I do leave my current setup on standby and can stand the $30 or so it costs me for the privilege.