What would be data source? Relays are supposed to search in their DB. If your relay only does NIP-50, you shouldn't have any data (or you save events from other relays)
Discussion
Yes, if you pay, the relay goes hunting for your events plus the events from your social circle, and maybe one step beyond that, similar to Followers+ in nostrgram.
It would make sense to get a full set of metadata, but that's relatively small.
