Sometimes fellow reefers might be getting rid of rock themselves on the forums if you're looking for a good deal. Are you averse to starting with dry stuff? No unwanted pests that way. Just time to build up the purpley goodness.
Aye, that's what I did. Works well but you have to be more patient. If you do go that route, maybe grab a small rock from a local reefer's tank that looks clean and scrub the crap out of it in front of a powerhead in your tank. Good way to seed coralline, though it will grow on its own everywhere regardless.
I started my new tank out with dry rock from BRS. It's a good way to avoid any unwanted pests. It really didn't take very long for it to turn purple with coralline. The porosity of the rock is great and you get a lot more for your money.