Live rock is the basis of the filtration in a SW
system. If you don't want to pay the prices that your LFS
is quoting you look online. There are a lot of vendors out there. Any LFS
that wont let you select the rock you want is not worth doing business with at least on the rock. I have been out of touch in the hobby for a while but Marcorocks.com was a great place to get excellent rock. I ordered from him and was happy with my purchase. There are vendors on this site that offer rock. Check them out.