That does seem to be a good solution, thank you for the recommendation!

Running an AS and obtaining a /48 through a sponsoring LIR seems to cost about $150/year in my country, but hardly anyone (except hosting providers and large companies) does this, since self-hosting, especially more complicated stuff, isn’t really that popular here; people are mostly uninformed that it even exists.

But route64 is apparently completely free (donations are welcome); they provide a /56 PA-like IPv6 block carved out of their PI, and they also handle BGP stuff, and I don’t even have to pay for any of this - overall, a great choice, considering my constraints. Anycast to multiple tunnels costs money (maybe that’s what you meant with 2 EUR/month?) but that’s pretty much lunch money so it would be OK with me.