This is called "a Nostr problem."
The Nostr website advertises "a decentralized protocol that stands a chance."
It only stands a chance if it remains affordable for the average user.
If you force projects onto a pedestal with VC funding, that is called abusing your funding. You can polish a turd all you want, but unless that turd provides value, it's just a shiny turd.
When Google throws a billion down the drain, does it affect me? No. That's their choice and their money.
When Nostr devs throw their money down the drain, does it affect me? No. That's their choice and their money.
If you have funding at all, make it last.
If you want to know how much people are willing to pay, the answer is it depends on who they are and what they are paying for.
Paying for a relay at this point is a hypothetical option for most people.
The things you listed sound nice, but I think seeing is believing. You could charge $50/mo if the product is truly worth it. The question is how much value are users really deriving from the paid alternative?
Maybe I can't see the details end-to-end because they aren't built yet. That's fine, but it means you are responsible for marketing those ideas in a way that connects with future users/investors.
Don't place the responsibility of evidence on the hypothetically future users. Our evidence is using the protocol. A developer's evidence is zaps flowing through the network.
I would pay whatever I think a relay is worth, which is currently nothing.