It can be as cheap as you want, mine is self-hosted directly from the pc that spawned out of replaced components from my current pc (featured here in this photo) after i slowly upgraded everything. I just need to set up cloudflare tunnel (free) to ensure privacy to my real ip address. Mostly the cost are the electricity i spent to keep the pc turned on 24/7. Oh and getting your own domain name has its own cost depending on the domain name.