I would go with a used M3 with a warranty. Vipers car was a great buy, it has the best mix of lux and sport which is what you want. Call him up and have him take you for a spin this weekend. Definately a nice daily that you can take to the track anytime. Any car YOU buy is going to hurt your wallet for maintenance if you bring it to somebody to do it for you. If you want a cheap car to maintain buy a ford fusion or something lame. I dont know how oil changes and pads add up to 3K though? Must of been some other stuff in there.
Oh and the B6-7 s4 will be my next daily, if they were in the 20K range I would have one now. I love those cars, V8 and quattro is nice. Too bad there were not too many sold and they are going for mid 30s still.