That dynamat is expensive, yes. Costs ~4k to do two doors (inside and outside panel.)
Heavy- not really. It's as heavy as 3M mats at the most IMO.

we'll you've already mentioned the source of your problem- it's the tires =). what tires are u using? I have michelin xm1s (on a sedan, not a van though) and at >60kph speeds, noise is pretty much from the wind and not from the tires.