The user pays. You go to the relay website, pay the sats & then add that relay to your relay list in the client.

On certain clients (Damus on TestFlight) you can filter global by relays. This removes the spam.

Some good relays (I use them):

puravida.Nostr.land

Eden.Nostr.land

atlas.Nostr.land

Nostr.wine (this has a filter option, which allows you to see your trusted network on global too)

nostr.naut.social

Ideally you should have around 10 relays b/e paid & non paid