I see that some car audio buffs use "flashtac" weatherproofing tape from Bunnings as a cheap alternative. Apparently it's "similar", it's a foil backed bitumen/rubber compound. It's available in rolls in a variety of widths from approx 50mm to 250mm.
I haven't used it, but I might inside my new doorskins, just as a deadener to stop drumming.
Cheers,
Mike.