You could do that, if you have a good local muffler shop that will cut and weld on flanges for a good price.. like $50 or less. Going that route you won't have to tune or anything.. it will be much cheaper, and change the sound/volume of your exhaust will be fairly significant. On the flip side, there will be virtually no performance gain with just the catback.. installing an aftermarket turboback exhaust and getting the car professionally tuned will result in a significant performance increase, both in power, and drivability. A good custom tune should be healthier for the engine, improve fuel efficiency, as well as increase and dramatically smooth out power delivery.