I bought the SecondSkin 40LB pack and wasn't disappointed. I still have about 1/2 from a full coverage install.
The 40Lb-er is b-stock so a few pieces might be a little slim or have bare foil spots but its a good deal for how much you get.
SkyHigh has 120mil that is great too.
If you're on a budget, massive posted roadkill and that will do fine, its just not as thick as the others.
I did also see some no name butyl deadner on ebay for cheap.