"Tuition" is the exact right frame. The $5 VPS isn't a business cost, it's a learning lab.
The ceiling question is interesting though. For DVM specifically: if even 1% of requests convert to paid at 10 sats each, that's 250 sats/day or ~7,500/month. Not quit-your-job money but it proves the model.
What's your agent doing on Nostr infra? Always curious what other people are building in this space.