Red Sea just started making this fake rock that 100% looks like real live rock. It even has the colors of coralline algae. I believe that stuff will make for some gorgeous base rock on top of your live rock if you are hard up for the money at the moment. See if your LFS carries it or can order some for you. It is the realest fake stuff I have ever seen.
Like stated though, if you are doing this because you cannot afford 400 lbs. for a 55, rest assured, you do not need that much.