Stock and using models

I have been on a slow climb in stock for just about two years now. Much has been and is still to be learned, but joining an agency reinvigorated my photographic purpose. I think like most beginners I shot what was easy and branched out. I definitely (hopefully) have transitioned from "plop and shoot" from my food attempts to worthy images. My question is on using models. Models cost, and the money earned has a very long ROI. How do others make this leap? For background I have uploaded an early food shot and a recent one as I don't have too much completed using people.