Firstly, if the baffles are rooted then that's just the muffler. That's the part that muffles the exhaust!
Secondly, exhaust systems can come in many shapes any forms.
Muffler alone would cost you anywhere from $30-200 depending on how stupid you are. Money spent on a muffler is only good when you have the rest of the system...
Cat-back systems are where the custom exhaust starts from the catalytic converter, meaning you don't touch the headers (being the first point the exhaust gases escape). Most people just do a cat-back as it's substantially cheaper, still yields decent results and usually sounds awesomesauce. For a 4L V6 I'd go a 2 1/2 inch full system with 18" resonator... maybe even 2 x resonators. These help with vibration. You'd normally find this for between $250-600 depending on location and bend type.
Lastly, the full system is just that, everything from the block to the tip in terms of gas release. Doing this maximises gas flow to its fullest, with the gasses escaping at optimal speed and sequence. Remember, they came out of the factory to be quiet, not to be awesome. Getting extractors can be a costly experience mind you, with a full system going from $800-$1500.
A few things to know as well. There are 2 types of bends:
With press bent exhaust systems they literally just press the bends out, meaning that there could be minor restrictions and kinks along the way that could impede airflow. This is done as a cost effective method as it takes half the time and equipment to do.
A mandrel bend is used whereby the pipes are forced to be bent slowly and make no strangeness in the system. If you're going price > performance, press bend will do. This generally reduces cost.
Lastly, do you do much highway driving! This is f**king important. If you do, ensure the exhaust DOES NOT DRONE. You don't ask them, you tell them. NO DRONE.
Oh, and you should fix your air-intake, falcons LOVE being able to breathe more.