I pretty much haven't bought any live rock, it seems live a rip-off to me, especially consideirng the quality you get.
I bought a used 120G that came witha decent amount, and added a bunch of base rock at about $2/pound. I managed to find some really nice looking pieces too.
I'd suggest just buying a few pieces of LR and going base on the rest. It'll all be live eventually anyway.
You should also be able to order base rock off the internet for fairly cheap. For example:
http://www.eco-reefer.com/