There is stuff at Lowe's or Home Depot that will apply like Dynamat, but it won't be as good. You would probably need 2-3 layers of the other stuff to equal Dynamat.
If you want quality sound deadening check out Second Skin.
I think the Home Depot or Lowe's stuff are roofing materials, something like peel-n-stick. From what I've seen posted, it's not very effective or worth the cost savings.
RAAMmat and Second Skins Damplifier series are really the only two options in my book. Dynamat is too expensive for what you get, even with ebay pricing, you are just paying for the name.