I got mine from my LFS, but had them order a few boxes when they were getting more in. They gave us a much better deal on the box price than if we bought it per pound (cured). It was uncured, but was fresh from the wholesaler that day.
If you do buy online, make sure you check the shipping charges and policies carefully. I know one buyer was really upset when he was charged box fees and extra shipping charges. It had been stated in the online store's policies, but those policies were buried and hard to find. The site had kind of alluded to free shipping, but it wasn't really free.
As live rock is the basis of your system, I think it's better to get great rock than to get poor rock for the sake of saving a few bucks.