What are the best cost effective or cheap ad networks for makers or early stage B2B SaaS companies?

Hi everyone :) I wanted to ask the community about ad channels/networks they've had experience with and have had good success with decent costs in CPC's/CPL's outside of the traditional networks like Google and Facebook. I know of the top directories but any other niche-specific channels they know of or can share would be awesome to know :) Cheers :) Dan