If your tank has cycled all the bacteria is there that is needed to inoculate your dry rock which can be obtained cheaply. However you will be looking at bear white to gray and light tan colored rock for quite some time before anything grows on its surface. Even then you will need to import some coraline algae either with some live rock or with something else covered with coraline, like a friends coraline covered power head or even some hermit crabs or Turbo crabs with algae on their shales. You will be waitings months (possibly many months) for anything but algae to grow substantially on your rocks though.
