Just start at one fish store and then go to the next. Live rock comes in a million shapes and sizes pick the sizes and shapes that will fit your tank and the look you are searching for? Most of the local fish stores will make you a deal on anything over 100 lbs. Best bet is to start by purchasing some large unique pieces to make up the base and then the really unique full of growth pieces to top it off. Sometimes you can be taken because some of the liverock around is concrete or it feels like and isn't very porous.