It better be real cheap. HAHA!
Here's my thoughts. A proper complete chain kit with the upgraded RS4 metal guides is about $1000. Labor to pull the motor and put it back is about the same, I'm guessing. It is an interference engine so you're looking at some valve work no matter what. I figure about $800-$1000 there.
Since the motor is out, I personally would break it down and tank the block, change bearings and rings, rebuild the starter, alternator, AC compressor and everything else down there, put all new gaskets and seals in and have a brand new motor when done. The extra cost isn't much, considering everything else you've just laid out for. Maybe another $1000 between parts and shop costs. That's if you can do the rings and bearings yourself.
You're looking at a chunk of change there. You have to decide what it's worth to you and what you can do yourself to save money/garner bragging rights.
2008 S4 Cabriolet 6-speed manual 1 of 2 in US