The problem with that is that the tuner exhaust will likely eat up your entire 8K budget in one sitting. To get any big gains off exhaust you have to do more than just a muffler. The engine management and other variables are different on the twin-plug 3-valve E430 than on the DOHC 6-cyl. Were it a V6, the swap would be easier. Still, by the time you purchased a E430 motor you are probably way over 8K right there, to say nothing of install and post install troubleshooting. Plus, then the resale of the hybrid would be lower and harder to sell period.

Hope this helps...Lee