First you need to take care of the car problems: Rear motor mount and Diff. mount (about 350$ used or 500$ new)
Oil Catch Can (used 80$ new 150$)
Next would be the performance parts:
Sort Ram Intake (125$-150$ used or 200$ new)
Turbo Inlet (125$ used or 200$ new)
Bypass valve(80$-200$ used or new 140$-300$)
Test pipe or downpipe (80$-400$ used or new around 600$ for a catted downpipe)
***Cobb Accesport: (used 450$ or new 600$)
If you buy the Cobb AP the fuel pump internal is a must(400$ new)
And i would definitely go with some coil springs to get a better handling and look for the car,my choice would be Eibach Pro-Kit(150$ used or 300$ new)
There's a lot of these parts available (used) in the "For Sale sections" of different MS6 forums.
Have fun and keep us posted on your mods!