I have a '98 A4 2.8Q with 92K miles and I am the original owner. I had the
TB, WP and tensioners done at 72K all to the tune of around $1000. I have
had the radiator replaced (with some hoses) to the tune of about $700.
Various oil leaks - $600. Recently I had all the fronnt upper control arms
and tie rod ends replaced to the tune of $1300. The mechanic says the oil
leaks are back although I have not noticed drips on the garage floor or the
old smell of burning oil as the leaks dribbled onto the exhaust pipe.
Mechanic also said front pads and likely rotoirs needed replacement and
quoted about $500. I will do them myself for a fraction of that (this would
be the second time they've been done - the rears I did myself once). The
sludge problem is an issue mostly with the 1.8T IIRC. Audi has sort of taken
care of those engines that have been more or less trashed as a result - I
say sort of since my understanding is you have to have meticulous records of
oil and filter changes at exactly the recommended intervals. Just for that
reason, I would stay away from the 1.8T unless it's been maintained by the
book by the dealer. Also, without a chip, the 1.8T of those years in the
quattro version is a bit on the slow side. With a chip, it will be peppier
but will likely have been driven hard too. One thing I didn't mention is my
cruise control doesn't work. I haven't bothered to track down the problem
since I don't use it.

Price for one of these? I'd suggest looking on edmunds.com and check ebay to
see what similar cars have sold for. I suspect mine might be worth around
$5K.