Have you considered doing a paid relay? For it to be economical, you'd need to start small, and you'd also need to it to be reliable as it scales. I really like nostr:npub1fyvwkve2gxm3h2d8fvwuvsnkell4jtj4zpae8w4w8zhn2g89t96s0tsfuk 's approach, I paid a good amount for them for 2 years. I'm curious if they're in the black.