[lcstorc]

That is a crazy price IMHO. Maybe I would buy one medium size rock and hope things move from it to the others in the tank. It very well may. I have been told sponges cannot stand the air even for a brief time so if I was told correctly those are not likely to live.
Another thing i can't help thinking is if it is that heavy how porus(sp) is it? Generally you want rock with lots of air space for the bacteria grow. I would think that rock would be lighter.
Not totally sure on that, but bottom line, at most, I would buy one rock at that price, and I would probably not even do that.