I would not necessarily go with the cheapest live rock. It is such an important part of the system I would really look for quality before price though of course price always plays a part. Particularly since you are going FOWLR for a while you could go with some LR and some "dead" rock. The LR will seed the other rock with the good bacteria, it justs takes time. Do you ever venture over to Orlando? I work there and could easily bring you some base (or dead) rock that has been in my fuge for about a year and has a good bit of life in it. Or your lfs may well sell base rock and you can buy some there for much less than LR. I have gotten some beautiful pieces from my LFS including a piece his 2 year old daughter sold me. (She kept saying how pretty it was and then I looked.
) If the "cheap" LR is coming from someone's system who is tearing down or something then go for it. It will likely be great. What you want most of all is porus rock. Don't worry about pretty colors or corraline just yet. That will come with time. You want as many crevices etc as you can for the bacteria to populate.
Ok I have babbled long enough. I hope you have a great weekend and hope that mr fire fish remains in good health.