Laptop/desktop wattage varies with processor and peripheral load. Unless you are pushing 10gbit and leaving the screen on 24x7, even an old box will be mostly in an idle state, with actual draw well below 30W.
Even if that were not the case, paying an extra $2.50 / mo to not do ghetto fabulous bs with rpi and vlans seems like money well spent to me.
10W running 24/7 means about 7.3 kWh/month. In my area the average kW/h costs about $0.13 CAD
So a good rule of thumb is that every 10W 24/7 is about $1CAD/mo.
So assuming 30W for a laptop and 6W for a pi4, that means a difference of $29/yr. Which isn't a lot but isn't a rounding error either.