stiff and clunky steering - going to be expensive??

[twitch]

Hi,

The steering on my 02 plate A6 has started to get really stiff when I've been driving for about half an hour. It starts to feel a bit juddery and a few times I've noticed at junctions if I turn the steering wheel there is a clunking noise. Does anyone have any idea what it might be?? It also seems to be worse in warm weather but this might just be my imagination.

I've just read quite a few bits about ball joints failing with catastrophic results and am very concerned now that it might be this. If it is this, is it expensive to fix??

A worried Twitch