You have to set yourself realistic expectations of what you'll get out of it in the end.
I've recently bought a dev's app and kept him on board with a % share of ad revenue. ( + cash milestones until the advertising revenue is significant enough )
Just need to find the right person.
We made an initial call, I've pitched him several different structures of compensation and let him come up with a price for his app that he was happy with, then struck a deal the following day.
There's a few reasons the reason it got done so quickly, we both had worked with the same people within the niche.
I've also explained to him my strategy upfront to get the app back on the road, so that probably helped.
You just need to find the right match.