Remember to make sure you have a place to cure out that 200 lbs. Not sure if you ever cured rock or smelt rock curing, but it will stink you out of the house. You are going to need to cure it for awhile, so as coast stated, sometimes better getting some cured from a fellow reefer.
In regards to places to buy rock, there are so many you just need to look around on here. People always posting about rock.
It is best to get different types of rock so that when you aquascape it, you can have some flat and branch and large pieces around.
In addition, are you going BB or DSB.