can you postpone the wedding? prices start falling after mid-august.

Yeah OK better book them tickets now lol, thought maybe some fast train service I didn't know :)
@magnifico bit late to postpone the wedding now the invitations have all gone out lol

HKexpress or Dragon Air (via Cathay Pacific) might be your best bets as some have said. Check out SkyScanner for cheap flights too. They do an Android app.

i almost forgot: taobao. They are a tiny bit cheaper than usual booking sites. At least for domestic flights

One other thing, changing the flights by a day or two can make a big difference. Mon and Fri can cost more depending on direction.

Guangzhou to Kunming by train is 25 hours.