NSX. Fast, light, cheap.
I'm also partial to the M5, even though it's quite heavy stock.
The ZR1 is brilliant for the money, but really requires RM to get the most out of it - don't know if minimal tuning only applies to non-RM cars for other people.
Overall though, the problem with this approach is that later A-spec levels are very hard to beat without extensive modifications so you are essentially forced to buy expensive race cars to be competitive.
