Not sure what a pi4 uses, but my NUC (16gb ram, 1tb NVME, quad core i3 up to 2.4ghz) running my smart home (HA in a VM) and a few other small services in LXCs uses ~7W on average. Loads more compute power if I need it at half the price. Even if a pi4 draws half the power, that's only $8 saving per year.