There are alot of online retailers that have good deals on LR.If it were me,I'd order 1lb per gallon(75lbs for your tank) of the cheaper Fiji base rock(not dry/dead rock).Then go to your LFS and hand pick a few select pieces that will help in the construction of the aquascape.I really like the Tonga branch rock,it allows you to build arches/ledges and it keeps the LR spaced apart.You really only need 1lb per gallon but you can add 30lbs of the Tonga branch to help build that aquascape up high.One thing you want to avoid is a rockpile.Keep your rock well spaced apart so current will be able to flow through it.