Look on classified sites such as craigslist.org, etc. I have seen it used for as low as a dollar a pound in some cases. When people's tanks break, they need to get rid of rock in a hurry, and they will post it wherever they can.
You can also save $ by buying base grade for stucture and bulk, them facing it with premium pieces. Liveaquaria carries fiji base live rock for $60/35 lbs.
You could get a couple live rock and get the rest dead base rock.But it take a while defore the other rocks become living.You save lots of money.Add supplements calcium stonitum i use orion too.