In reply to SeasonalDrip:
Linn of Dee is a £2 contribution and despite the signage not being entirely clear (it states £2 for a days parking)I'm pretty sure someone from NTS stated they did not expect people to pay for multiple days.
The ski centre ask for a contribution, again around the £2 mark.
I parked at the sugar bowl for my last trip and i'm pretty sure there was no contribution asked for, or if there was i didn't notice it.