Dynamat saved my sanity. I had Dynamat Extreme installed on all 4 doors and the cargo area. I can't believe what a difference it made not only with rattles, but also the overall noise level of the truck -- it's as quiet as a Lexus now.
Was it worth the price? I think so. I bought 2 packs of bulk Dynamat off eBay for a couple of hundred bucks. Installation cost me a couple of hundred more. It's hard to remember because I had a whole bunch of stuff installed at once, but I don't believe that portion of the bill was more than $500 (labor and Dynamat).
My only problem now is that it's sometimes hard to hear emergency vehicles approaching. The insulation seems to muffle the sirens!