Granted this is nowhere near PEK...The absolute cheapest thing that I know of still working is the NW C3 fare from CMB-YVR. Unfortunately it does not allow stops in SIN/BKK or NRT like the CSPL. Last I looked it is roughly US$800 one way, routes on UL for the first/last segment to/from either BKK or SIN and then all NW metal from there. Dushanthi at Carsons in CMB can issue this for you, PM if you want contact info.
If you want something closer to NAsia, I'd look at MNL, TPE or ICN, although it's going to be more than $800. I think Hainan had some cheapish fares via their PEK-SEA service, not sure if those were available one way though. Good luck.