Exhaust won't help that much for the dollars spent. I would fix the deficiencies first before going after more performance. So here is my 2 cents worth.
1) Upgrade the shifter.
2) Get subframes. This will save you from sticky doors, body squeaks, and will help in the handling.
3) Get a handling kit, even a level 1 type of kit from Steeda, Maximum,
Eibach, etc... Rear
control arms and new shocks work wonders. A coil-over setup is even better.
4) Get a cold air kit with a new tune.
These changes alone are worth quite a bit in the performance department. You will think you bought a different car and it will be so much more enjoyable.
Once you get past that, save your money for a supercharger or turbo kit. You could spend $1500 with all sorts of minor upgrades and pick up 30hp. Although gears are the best bang for the buck, gas is really expensive and unless you run lots of 1/4 miles, you don't want to go above 3.55's in my opinion for street driven car. With the stock gearing, you won't get out of 3rd gear in a 1/4 mile since you hit 110mph at 6400rpm's or so. With 3.70's, you will get about 110 at redline in 4th gear I think. It's been a while so I'm guessing here.
I can tell you that a
vortech s/c with a steeda tune will get you around 350rwhp, a totally streetable and well running car, and can use the stock exhaust. Changing the exhaust and headers were worth 20-30 horspower in that setup. Throw in bigger MAF, and I saw about 410 at the rear wheels.
Later upgrade the heads, cams (go Livernois here, saw 643rwhp and still working on it), and go nuts.