yes, i would think a 13 year old could help pay for trip as well, like what ever he puts in you will match it ? or you will double it ? one time our 13 year old or younger i cant reemmber how old he was, but he used an instrument from the school and would bring it home, he usually did well and took care of it, well, one day his room was messy and a hole got put in his bass fiddle, well of course we have to pay for it to be fixed, but we felt he needed to also pay for it , so we decided to help him make the money to cover the cost, for it, he too wanted to help pay for it, we went to like sams club and bought large quantities of candy bars and he sold them for a dollar each, he went door to door in our neighborhood, and into businesses, and sold enough to cover the payment of the fix which was only about a 100 dollars, the school said they would cover the other hundred, but he was proud of doing it, and the school loved that he took the effort himself to help fix it, but for a fun field trip, i would say sure its ok to have him pay for some of it, it does help them, to see how to pay for stuff, and do appreciate the hard work they may of put in , but in order for it to work, you need to let him do it, like if you want to go, this is the way it is, in our situation we never bought any candy bars from him, he did it all himself, we were very proud of him for this, and it raises self esteem too, just have fun with it, and i would say if you want to go , your father and i will match whatever you make, just enjoy life, nad have a good day D. s