I have a 120 and only have 50 pounds of pukani, and a few pounds of live Totoka from a LFS. I'll try to take pictures when I get home.
It's hard to give you an accurate assessment, since everyone has their own taste when it comes to aquascaping. Seems like more folks are going with the minimalistic approach, and if that's the case with you, I think you could get away with as little as 30 pounds. As others have mentioned, this rock goes a loooong way.