Facebook is an OCPM platform.

This means it prioritizes attention, and sells that to businesses for profit.
The bid in the auction is determined by Budget and Estimated Action Rate
If you want to get cheaper results, you have to get a better Estimated Action Rate
The absolute best way to achieve this is with a better ad.

Audiences: restrict the scope of where each ad's lookalike audience can find good impressions
Tactics: short win methods that don't build long-term success