Performance mods for the ST, in order of cost
If you want to keep the stock intake, remove the silencer tube. $0.00
eBay intake appx $40
JBA spark plug wires $80
Throttle body appx $100 or so
Larger MAF appx $200
ASP U/D pulleys $300
Off road Y-pipe appx $300
Hi-flo cat appx $300 or so
XCal2 $379
Nitrous Oxide system, $500-$1500 + install
Explorer Express XCharger $4000 + install