I don't mind paying for a subscription, as long as I'm not also paying for the privilege of being locked in to a specific vendor. If I pay for a subscription and then your prices quadruple or something, what are my options? Can I self-host a relay? Do I lose features if I do so?

I'm not affiliated. From what I understand, they provide an open-source implementation of the relay server: https://github.com/n0-computer/iroh/tree/main/iroh-relay (which may or may not be what they actually run as part of their hosted offering).

If you use their offering, you probably get some kind of web interface for metrics that isn't open-source.

Yes you can self-host your relays. Forever! Please check out the docs & hosting pages more information:

https://docs.iroh.computer/concepts/relays https://www.iroh.computer/services/hosting