13 year old wants to go on week long trip with youth group?

My 13 year old son wants to go on a week ong trip, white water rafting, with tree house ( a teen youth group) He is one of the youngest kids that go to tree house. I have my fears about letting him go. What if he gets hurt, or worse. Isn't white water rafting dangerous? They only give you a weeks notice, and the trip will cost 110 dollars. For me, thats a lot of money. I don't want to make him feel like I don't want him to try new things. I don't want to diapoint him. but first off, I fear for his safety. Secondly, I can't really afford to send him. I do realise that It could be a very memerable experience for him. I want him to have these kinds of experiences too. What would you do?