Get some off Ebay for starters. It's alot cheaper on there than in audio stores. I bought 100 square feet of "FatMat" which is basically a cheaper version of Dynamat. I think it was like $100 with shipping. You'll need a razor knie and some sort of roller to push the mat into the small crevaces. I highly suggest you use a hair blower while using the roller. This will ensure that the adhesive doesnt come loose after a short time. if you have anymore questions feel free to post them.
BTW here's a couple pics of my handiwork. This was my 1st time doing it also, so I'm no pro at it either.
I used Dynamat original in the front doors and RaamMat in the trunk and rear floor. I used a heat gun on the Dynamat. The RaamMat sticks pretty good without heat, but heat insures that it sticks really good. I got 62sq ft of RaamMat from eBay for $75 shipped.