I might pay 5-10k sats/mo. I generally hate the concept of renting software. It would be nice if the software was free or a one-time fee and you just charged for the service(s) you provide. Even if you did that, though, it would have to offer serious advantages over the free Nostr clients.
Discussion
I think a better long term strategy might be to offer software/services to content creators. If my income depended on Nostr, I would have no problem comming up with cash to support tools I depend on. There are quite a few features that don't exist in most clients that would help creators.