Two weeks is an incredibly long time to take another kid. I'd figure out how to pay the $80 and communicate in advance next time. I think a day of chol hamoed camp costs just about as much in order to be able to work if needed.
I'd just find the money from other places in your budget and make payments in installments if you need. But $80 should be manageable especially if you haven't fed the kid for 2 weeks.
