This is from adrenaline's terms and conditions posted on their website:
"
Vouchers purchased on or after 1st December 2017 will remain valid for 36 months from the date of purchase subject to the following;
- If the Adventure Voucher is not booked and taken within 12 months the amount paid for the voucher will be preserved for a further 24 months but the adventure supplier will not be obliged to offer the adventure nor to offer the adventure at the same price.
- After 12 months, if the price of the adventure has increased, an additional amount will need to be paid at the time of booking.
- After 12 months, if the adventure is no longer available, the value of the voucher can be used on another Adrenaline adventure."
Adrenaline themselves don't provide the service, think of them more like a booking provider. Given that the vouchers are 'good' for three years, the prices can only change after 12 months, and the terms indicate that any price rise is at the direction of the actual adventure supplier, I would expect that the ability to raise the prices is fair - so long as the amount is reasonable. Business costs increase over time, and in an industry heavily reliant on ensuring insurance cover remains in place (you're jumping out of a plane, the capacity for things to go wrong is high) a $60 increase may not be unreasonable.