Second that. 300 lbs of rock is not as much as it sounds like. I always thought 1 lb per gallon seemed like quite a bit of rock, but even in a tank my size (46g), it leaves the fishies plenty of room to swim. . .especially since most reef fish are used to having a lot of rock for hunting and hiding.
Oh, and base rock is the same as live rock, except. . .not live. In other words, it's been dried out and has no life on it, but it's the same type of rock otherwise. Not only is the rock itself significantly cheaper, but if you order it online, you save quite a bit on shipping since you don't have to have it express mailed.