I did lol at cheap kwh internet - sounds way better than talking energy costs

Older desktops can have a somewhat hefty idle power draw due to the overall system consumption contributing more than expected, such as the southbridge. According to this old review of the i7-2600k, the system idles at 74w, which at $0.12 per KWh, would cost you roughly $77 per year. Though you might want to confirm that with a Kill-a-watt meter if you can (libraries sometimes lend them out), since I'm pretty sure that total system power chart includes a discrete GPU, so the real number for a GPU-less system is probably around 40 or 50w at idle.

If that is accurate, you could potentially replace your i7-2600 with a used Dell Wyse 5070 thin client from ebay for about $40 (in the US), and that idles at 5w, which would only cost you $5 a year at the same rate.

Older thin clients and laptops tend to have much better idle power draws compared to desktops. For other people reading this, if you're using a desktop for a low-power use case, it's probably worth finding out what its idle power consumption is and doing the calculation to determine if it'd be worth replacing it with a more efficient used thin-client or office mini-pc.