To save money, they can go the derelict laptop route.

If they get a low tdp board, maybe like an old laptop without a battery, the power difference isn’t going to be too much. Pi can pull 9W at full tilt. And an old Ultrabook with it’s monitor tuned off or unplugged can probably pull 35-45W at full tilt.

So 45W - 9W = 36W

36w x 24hr x 356 = 315,360Wh

315.36kWh x 0.25 cents = 78.84 a year

But that’s assuming everything is running at full speed. For something running 24/7, we can probably estimate idle state is more common. Laptops can idle about 3-4W a pi4 is also idle around 3-4W.

So 90% at 4W and 10% at 45W for the laptop

And 90% at 4W and 10% at 9W for the pi

Gives us 8.1W average for the laptop

And 4.5W for the pi

Giving us a total difference of 31.536kWh. or 7.88 additional a year.

This is also assuming the laptop has the same computational power as the pi, which isn’t true, so the laptop will end up finishing tasks faster than the pi and use more power for a shorter amount of time.