Originally Posted by mkoesel
And don't forget the M3's little brothers - the 335i and 135i. Not to mention the G37. These would probably be the worst performers among the others you mention, but they are also by far the cheapest.
For that exact reason ($$$ and tunability) I just euro-delivered a 335i. I have an S2000 -- it is VERY hard (albeit very fun) to use all the high end HP of a low torque, high HP engine. The torque-monster turbo 3.0 L inline six will be a lot of fun.
When the M3 sedan comes out I will do my cross shopping and see whether it is worth the extra $20K to upgrade.