Well, hell, if you've got unlimited funds, why screw around with any of this junk? Get a BMW M3 or a Ruf modified Porsche GT3.
A base model Z roadster stickers at $34,450.00
A base S2000 stickers at $33,150.00
The G35 coupe base stickers at $32,750.00, also not available al fresco.
At least a GTO stickers $32,995 at base model. Of course, it's not available in an al fresco version.
A Corvette should be nowhere in the running with a base sticker of $44,510.00
Obviously, if you're looking for a roadster/convertible then the G35 is right out. The Z and s2000 are the only true roadsters of the bunch. Obviously you can get a drop top Vette but it's going to be a heck of a premium over the Z or Honda.
As mentioned earlier, you need to know how to drive the s2000 to squeeze the fun out. If you're used to driving torquey Mustangs that pull from 3k and try to drive the s2000 that way, you will be disappointed. A normally aspirated 4 will simply not deliver low end grunt.
If on the other hand, if you keep the s2000 shrieking at redline, you'll be hard pressed to find a substitute for the nimble little roadster at a price that's even close. Even with the smaller 2.0 liter that has been ditched in favor of the 2.2, the 'weak' s2000 bested the 350z in the above article in every performance category. With more power on tap at lower revs now, the s2000 should post even better performance stats.