Cheap hostels in China

I with my boyfriend are going to travel 2 months in China (backpacer, budget travelling: Yunnan, Sichuan, Shaanxi, Beijing). I look for the way to find cheap hostels.
Could you recommend me websites/applications that are useful to find cheap accomodation?

What do you know about Hosteling International? I've heard that there is some loyalty card. With the card you will get some discounts. How/where can I buy the card? What is the cost of the card? And later - how to find hostels united in Hosteling International?