Our family, four of us, need to buy a cheap economy return ticket from PVG to PRG (Prague).

I've checked on http://matrix.itasoftware.com and a cheap fare on ChinaSouthern (actaully operated by KLM) is there--but I'm not sure where I can book it. Skyscanner does not find it. Booking the same flights on KLM.com costs more.

Any suggestions on how to book this?

Any suggestions on how to get cheaper tickets?