I like it, I wonder if they're running this for nos.social app or if the name is a coincidence... It's elastic search so yeah, it could get spendy depending on how much your retention is, how many relays you're scraping and and query loads are ..

Clients could also just have a local db since they're constantly scraping the relays too... Except web clients they're kinda stuck with crap for a db in the browser.