Thanks for the replies.
Ironically, I got a letter from Audi a few days ago asking about extending my warranty and breakdown cover. They didn't include any prices, just a number to call. I haven't called them yet.
If the prices you list are anything to go by, then I won't be renewing. There's no way I can afford £835 for a years cover. I'll just have to take my chances.
The prices for renewing just the breakdown cover are reasonable, but still higher than what I can get through Tesco.