hahaha Philip ~
Basically, dynamat is not cheap. Dynamat extreme (which is the best for stiffening as well as damping, more for audiophiles like myself) retails for ~$40/10ft^2 IIRC. I used 3 of those to do the trunk/trunklid of my coupe, but honestly it wont make a huge difference in exhaust noise, and was done mostly to clean up my bass (from that stiffening I was talkin about).
If I were going to go nuts on a new shell, I'd do massive prep (search) and lay on some eDead from Elemental Designs.
http://www.edesignaudio.com/edv2/index.php?cPath=1_24
This stuff will get into all the cracks and such, and will do just as good a job as Dynamat if you prep well for about half the price. PM me if you have any specific questions ~