I'd say get a nice set of rims first......make the car look good, and get some good rubber b/c if you're serious about getting performance out of your car, you will need good rubber to run around on or your car will be fast, but it'll get you killed....

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and the price for the exhaust sytem sounds pretty okay.....'cept don't believe them about the performance gain....unless a car was VERY badly designed from the very beginning, you can't 'release' that much power just by letting the engine let off air more easily....expect somewhere around 5 - 10whp max gain....depends on the actual setup and also depends on your car.....
and yeah, when manufacturers give numbers, it's at the flywheel....you'd probably dyno around 100 or so, depending on your transmission...
either way, just do research before you get stuff and see if anybody else on the forum has the same kind of car and what they've done
happy modding! 8)