The S series of the Audi's will carry much more WOW power than the A lines. I did a quick look in the Autotrader - in Canada an 05/06 S4 is going to set you back just over $50K. In the US however, it will only set you back $35-$40K US. That will be right in your price range next year.
http://www.autotrader.com/fyc/vdp.js...l=&cardist=425
I read that Audi will be redesigned in Europe for 2009 and that design will follow to North America in 2010. If you own an '06, you'll lose a lot of your WOW factor when that happens.