Check the actual prices for days you wish to go, but my bet would be that flying from Western China is most economical. Look at CTU, CKG, and KMG since internal Chinese ticket prices are first based on distance then on discount level. The only way to get all the way there on miles is Star Alliance or Skyteam.

Good sites for internal China flights are CTrip and eLong. They will both offer the discounted prices but on the major international sites (at least until fairly recently) you'll only see Y fares.