The cost does not include the power consumption. For Intel-based Mac Mini running a network filter I suppose it will be at least its idle number 20 Wt or about

The cost does not include the power consumption. For Intel-based Mac Mini running a network filter I suppose it will be at least its idle number 20 Wt or about 200 KWt/year or 20 USD/year (using 10 cent per KWt as an average price in US). Using any kind of VM will bring that to 30 USD/year. This is a non-trivial amount. In Europe that may reach over 60 Euro/year depending on how a particular country is affected by the war. It is unclear if using an old Intel-based MacBook Air without the screen will be significantly better. While its idle power is around 3 Wt, running a network filter in a VM will wake the CPU up often enough to bring the totals closer I suppose to Mac Mini. Raspberry PI 4 on the other hand consumes only 6 Wt at the full load. Using it as a mostly idle network server brings that down below 1 Wt or 1 USD/year. MacBook Air with M1 may be closer to Raspberry PI numbers without using VMs, but those even with a broken screen I suppose are not that cheap. And running a network software in а VM there may again brings numbers to 10 USD/year or more.