Id start hitting that granite with an 8lb sledge hammer to make the size more manageable. Try stacking it up, you could silicone chunks together if you are worried about it falling. You should be able to make something pretty nice with all that.
When designing a new rock scape I use a bench and not a tank. Just mask out the footprint. That way I can stare at it over several days and tweak to my heart's content, then take pics so it is easy to quickly reproduce in the tank when ready.

Do you not have a local place to buy rocks cheaper?
You will not find (easily) holey rock much outside of Texas. Personally I don't like holey rock because it does not occur in the lake and it has rough edges that can injure fleeing fish. Plus expensive and hard to get. And white will get coated with algae. Just ask for any boulders...river rock or field stone for building walls. I have found phone representatives at these places don't realize customer service is a component of their job...better just to visit and browse.