I went and did a tiny bit of research on this. The new Mercedes SLK 350 starts at almost 6,000 more than the SLK 320 started at. (http://autos.msn.com/research/vip/jo...?modelid=11404)

If the 3.5 ends up in the xfire (which I doubt), I would be very, VERY surprised if the price didn't increase by at least 50% of what the SLK's increase was - I imagine you could tack an extra 3k onto the current price, minimum.

However, I doubt that the 3.5 could even go in our cars - remember the new SLK 350 is a completely new chassis as well, with a completely new transmission and drive train. The 350 has VVT, four valves and dual cams. The xfire would need a lot of mods to accept that powerplant (I think - again, I don't know everything, so I could be wrong on this).