For startup costs, ~80€ for a used micro PC a few years back (+100€ for a 1TB SSD for it).

Since then

• 6€/yr domain
• 48€/yr email (proton plus using domain above)
• I'm thinking of setting up Backblaze B2 for offsite backup, should be ~20€/yr for about 250GB stored continuously if I calculated right

I never bothered with electricity costs, since it's a small micro PC. It probably uses sub 20W average, which, next to an AC, fridge, and WFH costs, has to be negligible, the cost of buying a measuring device in itself is probably not worth it