Honestly they opened source their solution, 150 USD in nothing some big relays operators can't afford by joining their efforts and sharing the costs, especially if they make it available for a small fee like 1 USD a month. If nostr become a thing one day maybe some people will be ready to pay for it when kicked out of other caching service. Ideally Primal could allow his app to still work in "degraded mode" without any caching service though.