is this an existing tank or are you just setting it up? LR
rubble can be bought online as well. depending on your local fishstore, it may be alot cheaper to get it online. www.liverocks.com
is a great resource. Call or email them if you'd like and tell them you'd like the rubble, as it will likely be cheaper (i believe) than the regular rock.
In my wet dry, you can just remove the eggcrate that the bioballs sit on and fill the sump with more water to increase the level and put the lr