I bought my CPO'd RS6 last March with 38k on the odo. New tires, timing belt/water pump and brakes all around were done before I bought the car.

Since then here's what I've put into the car in less than one year:

$2,500 for a Euro RNS-E with BT (thanks TeddyB!!! teddybgame@hotmail.com)
$300 for new APR R1 diverter valves
$65 for the RS6 badge on the steering wheel
$600 front pads
$1,200 new tires (my fault for not rotating soon enough)

There's a $50 deductible for CPO coverage and I don't have an exact amount but here's what has been replaced:
DRC (2.5 times)
Drivers side combi valve hose
Cup holder
3 door panel inserts (due to peeling)
Drivers seat heating element
Brake light switch
Third brake light leds
CV boot
Drivers window control unit
Rear passenger speaker grill

I now have 75k on the car and it is currently on the rack at the dealership for the 70k service (TB&WP)....I'm also having the intercoolers cleaned, all the plugs replaced, the N75 valves replaced, an oil change and a tranny flush with a new filter. Right now just parts are $1,800 without my discount; adding labor I should be about $2,300 out the door.