Sound differs between mufflers. Usually exhaust systems like Greddy Evo sound really nice and have little to no noise and carry a nice deep tone to them. This varies between cars of course. But if you notice Greddy and most aftermarket exhaust companies their mufflers are not excessively big but yet not so small. Usually those style exhausts have a deeper to subtle sound. If you don't believe me next time your on the road... when you hear a car that sounds like a go-kart look at the size of their muffler. When you hear a car thats sounds more mean or atleast has a nice flow deep tone/throttle sound look at the size of their muffler. I know this based on experience and the variety of mufflers/exhaust systems I've dealt with.

Its cheaper to just buy a aftermarket muffler then have the piping done at a shop. A cat-back with muffler install usually I pay around $100-$140. A aftermarket cat-back system from well known performance companies would vary on price but usually anywhere from $300-$600 and possibly even more.

This is my take on this. I've always prefered purchasing my muffler and then having a shop do the piping.