Anyone can host an RSS feed with just a web server. Everything from a shared host to a VPS to a Raspberry Pi at Home. It takes a lot more resources and administration effort to run an ActivityPub server.

That's true of current implementations, but the spec is flexible enough to allow much simpler ones. You can have an outbox which is a collection of activities (that could even be statically generated) and software could poll the outbox just like RSS. Existing software requires a push-based model, which means handling follows, which means a database, but fundamentally there's nothing stopping ActivityPub from being pull-based.

ActivityStreams can be hosted in the exact same way, hence the "pull" model. It's not the same as ActivityPub, although the latter builds on it.

Or even a static website that you can deploy on many free CDNs, such as cloudflare pages, vercel or netlify.

Maybe that'd work too! I'm honestly not very familiar with ActivityStreams. My main concern is figuring out a lowest common denominator/the simplest thing that works, and I think RSS is sufficient. I'll have to do some more reading + thinking on ActivityStreams.

Doesn't ActivityStreams need query parameters, so won't work with static hosting?