We shouldn't start using nostr relays instead of databases with public APIs. Just because you can, doesn't mean you should. Remember blockchains?
Discussion
how much for the ICO?
A nostr relay is a database with a public API...
someone else's database that may or may not persist your data.
Isn't that always the case?
Not if you use your own database.
Still no difference
Someone else's database where you have no control over whether they persist data vs your own database where you have full control over what data is persisted are totally different. Are you being deliberately obtuse?
A public nostr relay is akin to a public database with an API.
A personal private nostr relay is akin to a personal private database.
I fail to see any difference.