How are people doing HTTPS?

I have a PC I have installed Portainer on, with various docker services (home assistant, jellyfin, etc..) with an ISP supplied router fixing various device IP addresses and reaching out to dyndns.

I really want to move everything over to HTTPS connections by supplying certificates, tls termination, etc .
The issue I have is self signed certificates mean I have to manage certificate deployment to everything in the house.

I figure I need to link a domain to the DynDNS entry and arrange certs for the domain. However I can't make the link function and everywhere wants >£100 to generate a certificate.

How are people solving this issue?