Premium aquatics has great rock for cheap I would recommend their Fiji rock if you are mostly stacking.
Manado rock if you want branching/arch structures too. When I bought it had extremely good corralline coverage too... Less dense than Fiji. Costs more but well worth it.
Again premium aquatics are great rock sellers and if you need certain size pieces or want a lot of Hitchhikers they will usually be able to do it for you if you ask.