When I flew jumpers, I got paid per head. Bigger plane, more jumpers, more money. The system worked well. I got $2 for each licensed jumper, $6 for each static line student and $10 per tandem. (we didn't do AFF).
It wasn't unusual to turn 2 tandems each load all day in the 182 and 3-6 in the 206 and 207. To this day, the most money I ever made in aviation in a weekend was turning loads for 12 hours straight on a sat and sun. Don't work for free, if you can't get money out of your DZ owners, negotiate free jumps and get your A license.