Dont know if this is any help or not mate,
But in scotland you dont need to go onto a campsite, as long as you stay away from the main roads, you can use the land to your hearts content,
Glen Nevis is alright, but they will rip the **** out of you money wise,
There is a not bad site in Inverness, called the Bught Park, but from there if you wish you have the heart of the Hills around you.
Or if you prefer, more basic is over on the east coast by aberdeen, there is some local council camp sites, but if you are going in Sep. Like others have said Take midge nets, and get some good spray.
Braemar,Ballatar, Aboyne, Aviemore, Turriff, Bannff, Inverness, etc etc, the list is endless,
Best advice, go out explore, and find what you want, and stick to it, you never know you may even get the other half interested.
The Hobbit