Audi A4 B6 (2001-2005) Questions & Answers

The window regulator and comfort module should be checked out.

The airbag light is usually caused by a connection under one of the front seats. It is a common problem... check out the fix on YouTube.

Hi Adrian. Only you can really answer this question!. Car Sales have this model at $5400 (auto) and $5100 (manual), but with higher estimated klms at 150k. So the price is not too far off the mark based on your body assessment and buying through a car yard. But do you have any history on the car, as 111K after 15 years seems dubiously low?
The only other thing I will bring to your attention is the ongoing running costs, particularly if things start to go wrong. Servicing costs is pretty much the norm, though replacing the timing belt and brakes discs for an Audi will set you back a lot when the time comes. But if (and when) you need to replace other parts, then things can get really expensive quickly. Audi charges a fortune for anything genuine. So if there is no after market part for what you need, for example engine mounts, costs can blow out to ridiculous proportions. Just need to factor this into your decision. Good Luck.