It probably greatly depends on what you plan to do with your instance.

My instance is just used by me and occasionally my partner and some friends. Running it costs me nothing aside from whatever portion my energy bill is increased by having the container active in my home server. I already had registered my domain for other things, but a domain is $10-$12USD/year, which is basically nothing.

Realistically probably less than 20 a month for a good cloud provided option.

With your own hardware, I ran mine for less than 1$ a month with an existing domain and hardware around the house. You dont need much other than storage. For single user probably next to nothing. For family and friends a bit more.