I see threads all the time about guys looking for alternatives to 'dynomat'! Well first of all it's Dynamat and second it's overpriced.
So what other choices do we have then? Well you could use peal 'n seal but it's thin, light, messy and can melt at high temperatures.
Another choice is called polymeric mastic which is used as a vibration control material for ducts and other industrial applications. In fact, you probably alread have something very similar on the firewall of your car already.
The mastic is EVA (ethylene vinly acetate) based and has a pressure-sensitive adhesive backing. It's ideal use is on flat surfaces as it does not conform as well to irregular surfaces like the other deadening products. The use of a heat gun and some extra adhesive is pretty much required for irregular surfaces.
The benefit of this material is that it is heavy and cheap. Here are more of the product specs:
Sheet size: 54" x 32" (12ft^2)
Weight: .7 lbs/ft^2
Temperature range: -4* - 158* F
Price: $14.62 per sheet before shipping; $1.21 per ft^2; $1.74 per lb.
I've used this successfully on the floor of my car and it works great for mass loading and also for some sound blocking. So if you are in the market for a deadining and don't mind putting a little extra effort into proper installation than these sheets are a good, low cost alternative.
You can find the product buy going to www.mcmaster.com and looking up product # 9709T39