Most engaging IG content you ever re/posted?

Hi,

I'm working on an experiment with FB ads and struggle to find a post that is able to generate crazy low engagement costs.
The goal is to find out what the best cost per engagement you could possibly get, is - basically the highest view to like ratio you could possibly achieve. It needs to be an image, not a video.

Glad if you can throw some ideas, already tried the shotgun method but didn't find something truly extraordinary.