When I took training at Wiley Post (PWA) airport in OKC, the owner of the
rental planes was the CFI and got the whole $20/hour for instruction. I had
a couple other instructors there and paid them similar and they also kept
the entire amount for training. The owner got his rental fees.

When I got some training at McCreery in McAllen, TX (MFE), I paid $25/hour
if it were their rentals or $35/hour for instruction in my own plane. I'm
not sure how much the CFI got of that.

I also took CFI's up in Iowa, again what I paid them for the instruction,
they kept. Some of the smaller airports with a CFI around usually aren't
working for a flight school or FBO and get to keep all they're paid. Check
out the bulletin boards (Not BBS!) at the airstrips...

YMMV!