Facility where mine trained at in the offseason would pay 3/4 high school catchers to catch each weekend. They'd hang out on a Saturday or Sunday and make a little money each session. They got to hit/lift for free if it were quiet, place usually had football or something on. It wasn't much but let's say it was $15-20 for an hour session? You do 5 over 8 hours, get to hit/lift and watch football and leave with $100 cash? Pretty good for the avg 16 year old.
I don't think I'd ever charge a teammate but I'd also be willing to say no if I felt it were too much. I'd just pick a set number of pens he feels comfortable with every week and wouldn't go over that.