Are you talking about simcard? I am confused by simcart, if so, there are three companies, China telecom, China unicom, China mobile. You can learn the detail on their website. The price range from 19 rmb to 500 rmb.

Three companies are in competition, China Unicom own the cheapest data combination, China Telecom is best for family, China mobile is for rich.

I prefer China unicom.