That is a very good price for live rock. You will not find it much cheaper at all.
To cure it, you would have to put it in a bucket of saltwater with a powerhead and let it circulate, doing water changes on the bucket every week until there is no longer waste and debris on the rock. A good way to know if it is cured is by smelling it. If it has a bad odor, you know it is not cured yet.
However, if the rock is for a new tank, the cycle of the tank will cure the rock and in that case, you will want to get all of your rock at once so that you don't have to cure a little bit each time. Adding it to a cycled tank in smaller amounts will recycle the tank.