I started on a TI-83 Plus with a program that helped factor quadratic equations. Before I knew it I was making games on it. What I would have gave to have had an iPad with all that RAM!
I went down this rabbit hole earlier this year. Best I came up with was to calculate the TDP at max for the whole year. Full TDP is unrealistic, but it gets us a worst-case "max running cost" . Energy for me is roughly $0.12/kWh, so the yearly max running cost for a 35W TDP is $36.79, 65W is $68.33, and the 95W would be $99.86.
I ended up going with a HP EliteDesk 800 G5 Mini I5-9500T (35W) off of Ebay for $100 and it does the stuff I need it to do just fine. According to my current monthly power usage graph, it's averaged 7W which accounts for $0.61 of this month's power bill.