Sanity check
"I" think your idea is perfectly logical.
I believe it will cost you more than 300-500, but to each their own.
You are definetly on the right track with maintaining your current gas mileage and increasing seat of the pants Fun.
I recommend a 60-1 turbo with a .86 exhaust A/R for your /6. You have good amount of packaging area with a /6 that is for sure.
Browse around
http://www.theturboforums.com/smf/index.php for some good information regarding your interests.
Good luck, keep us posted!
=P~