Depends on the size of your tank.. I am building a 220 so I ordered 100 pounds from reefrocks. That rock is ok, nothing special but by far the cheapest you will find.
I also ordered dry rock from brs (bulk reef supply). I ordered 50 pounds of tonga shelf rock and it is amazing. I cant wait to get my tank in the morning and start tinkering with the aquascape.
the shelf rock pieces are huge and probably wouldnt fit in a smaller aquarium.. I put photos on mu build thread.
MrPillow said:Premium Aquatics - Aquarium Supplies has some great rock in the clearance section for $1.50/lb. Not sure how much they have left so if you have a big order they might not be able to handle all of it.