I have a Vultr instance that costs me $2.5 per month. Pi-hole doesn’t consume too many resources. While I’ve not done any math, assuming I can handle 10 ppl browsing at the same time, my cost per person is 25 cents a month. Assuming other overheads(my time etc.) and some margin , I’d say a dollar a month ? For better effect , I’ll say 1.49 per month ;-)