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.