For bitcoin core node running?

Dandelion is probably the most advanced and well talked about protocol for transaction relaying, but that's significant IIRC, and no monetization.

There's no way to prove that transactions you relayed to another person eventually gets relayed to a miner. Instead of paying people for a possible service, IMO it's best to rely on the default bitcoin core logic which does it's best to ensure propagation while trying to protect privacy the best it can. Or to broadcast over tor to blockstream, mempool, etc. for privacy reasons. Perhaps you can pay them if you want but I don't think they'll care about charging for that.