reducing CPC for ads

does anybody have any useful general tips for reducing Cost Per Click

audience is primarily through emails and phone numbers of people who have already signed up for another service
I thought FB would make the ad cheaper but its actually MORE expensive

would it be cheaper if they have liked one of my FB pages?

I start some new offers from lasermediagrp com in FB now, but the CPC get so high that I can't earn money.
Interested in hearing this answer too.