Negotiating price to process birds

In the past I have processed a small (25) batch of chickens myself. I do not relish this task, so have sought out some neighbor kids to do it for me. I am having a hard time finding information on how much one pays to have birds processed (lots of info about how much it costs from chick to finish, but not *just* processing.) I would crate up live birds, take them across the lane, they would get the job done, and I would come back and pick up, probably some plucked, and others "shucked." I will do the packaging. These kids have experience killing and cleaning just about all manner of critter, and I trust them to do a good job. What factors should I consider when figuring this out? Can you give me a recommended rate of pay?