Yep, right around $7-8 for one at home depot here in Nebraska.
one tank should last MANY brews. some people remove the regulator when not in use, but mine doesn't leak at all, and honestly i think that's more a problem of the cheap manufacture of the throw-away tanks, than the regulator.
Definitely get the 22" stainless aeration wand. its AWESOME. don't just get the regulator and use aquarium stones.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10