...but are you comparing the 4.2 to an RS6 now or an S8? I am confused.

A 2004 A6 4.2 with perhpas 40k miles on it would probably still be around the mid 20s. I would imagine that the RS6s that are under the $35k mark are closing in on 80-100k miles...for over $10k more (at least in the 250 miles surrounding Boston). All the RS6s under 50k miles are over $35k in the same radius.

Oh, and if you are going to quote eBay prices, then look at the prices of some of the C5 A6 4.2s on there. I think there is a nice blk/blk 4.2 in SoCal for under $20k, and it looks very nice.

In the end, what are you looking at buying? DO you want an S8, RS6, or A6? If you are so convinced that a low-priced RS6 you found is a great deal, why wait?

Just keep in mind, it costs a lot more to do a timing belt on an RS6, they are also known for DRC failures, and they have had their fair share of tranny troubles. My local dealership's shop foreman talked me out of an RS6 when I was shopping back in 2006...too many issues and not enough support from the Audi on some issues makes it a risky bet, even if you find one with a CPO "warranty."

Also keep in mind that CPO is a marketing tool, and not a very good warranty. I've had personal experience (my former car) where the CPO was basically a rubber stamp from the dealer to charge a higher price, when they delivered a car that clearly should not have passed their inspection "process." The car had bald tires and I could not pass inspection...and tires are on page 1 of the CPO checklist! After that, almost every repair was a struggle with AoA to determine if something was wear-an-tear and therefore excluded from coverage.

Not worth it IMHO...I'd rather buy a used car and find a good aftermarket warranty than pay a premium for CPO.