Try Fish Town in Queens, good base rock for $3.99lb. Not much growth on it, which is good if your just starting out as you wouldn't have alot of die off, and they have some really large pieces which are usally hard to find.
WHatever you do bring a bucket with saltwater in in with you so you don't have to re-cure the rock when you get home if it is already cured in the stores tanks. Last time I bought rock I brought 3 5 gal buckets with me and after they weighed the rock it went right into the buckets and stayed in untill I got home which took about 10 minutes. THen I put it in my tank with no die off and no problems.
You shouldn't have to bring buckets , so you don't have to re-cured the rock, unless it's going to be out of the water for a couple of hours as the rock should be fine, also the rock mayn't even be cured to begin with. What you want to do is when you get the rock home place it in bucket or a rubbermaid container, with saltwater and either a power head or a small filter, and lets the rock sit for a # of days to make sure that it's cured. The rock from the store mayn't be cured so you want to cure it before you play it into the tank. You probably want to bake the rock also.