In reply to Jim C:
The Glen Nevis campsite is closed until March I think - we tried to stay there a couple of weeks ago.
I don't know if the same applies to the bunkhouse, but the pub/restaurant at the Ben Nevis Inn was only open at the weekend when we were there too.
We ended up wild-camping out near the Polldubh crags - theres some nice flat bits at the end of the road only a few meters from the car park which are quite convenient, can get a bit wet though. It's on a major path so you really have to take down and put up the tent every day but its close to the car and you can then drive to any of the Ben Nevis car parks easily from there.
Doesn't meet your requirements for electricity, and you have to carry the food and booze with you, but is free and has good access to The Ben.