Hi Dave,
AFAIK there's only one level of Appelcare. £329 seems a lot. I have bought it for my laptop and for computers at work. My home one was £180 this March for a 13" MBP. The ones in the office were a little more expensive. You can only get Applecare from Apple and they tend to control prices very strictly. Even at your quoted price, it's worth having the peace of mind, in my experience. Macs are great but cost a helluva lot when they go wrong, and they do.