When dampening sound there is rarely a substitute for mass. Thus the denser the material the better it will dampen noise.

You might want to look at some of the other dynamat "knock offs" - brown bread was mentioned on this or the other forum as being particularly good, I found it at this website along with some other less dense materials:

http://www.b-quiet.com/

Also, people have reported getting some good deals on dynamat on ebay. Most likely you would be looking for dynamat extreme, not the regular stuff.