The only expensive part is the hardwarevfor the elastic servers. Kafka is cheap to run. We have an on prem elastic db pulling in tens of thousands of events per second. On prem servers aren't that expensive. It's really just 6 servers with 20tb each and another 40tb for backups. And it's not like you have to store everything forever... Compare that data flow to everyonevwatching youtube all the time. It's really nothing...