Just what you are thinking is appropriate...exhaust, chip, and K&N air filters? The combo will run you between $1000 and $1500 dollars. You would be looking at about 20-30 hp improvement over stock. For serious power gains (anywhere between 306-330 hp), expect to spend about $10,000 for supercharger kit or a 3.8 liter stroker kit. Another route to serious horsepower would be a fully custom turbo kit, which I might perform if I decide to keep the car. But, as with all serious engine upgrades, other components, such as the drivetrain, suspension, and brakes should be upgraded as well to take full advantage of the extra power. Tuning firms for the Crossfire include Startech and Renntech.