Broken springs do seem to be getting more and more common on the A2 and for no real apparent reason.
THe spring material is a high grade steel, epoxy coated and should last easily more than 3-4 years. However, the top bearings do seem to be prone to seizure which could lead to extra lateral forces on the spring.
Overall, the Kwik Fit quote is good, although my experience of the work these guys do is not very good, especially their tracking ability. If you can get to a good independent specialist (Stealth Racing springs to mind!) then I'd recommend that option above a Kwik Fit fitter any day. The Audi quote is high because of their labour rates, but apart from that, it's not bad (although for that price, you could get a pair of Weitec front springs and get Stealth to fit them and have change left over, a lot of change!).
Cheers,
Mike