Where do I find the cheapest tickets for (if possible direct) flights from Bangkok to Kunming? Ctrip, China Southern and Air China all have ridiculously high prices (2000 RMB, close to what I paid for Düsseldorf-Bangkok), probably because they go via Guangzhou.

I believe they must come cheaper, especially as the flight is for 1 March. Any ideas? Also, I need to put a fairly large box (containing my bicycle) into the hold. How do I arrange this?

get on to Thai Airways' Kunming office. they often have deals which work out fairly good value. check the airline's website for baggage rules - every airline is different, and policies regarding bicycles are particularly difficult to deal with. watch out for words like "recognised" when talking about bike bags/boxes. i.e. it needs to look like a bike bag, not just be a bike bag by virtue of having a bike in it :)

Thai Air fly direct.
Price may be related to season.
Xmas is peak season for Thailand. Winter is high season for Thailand and January is high season for Chinese travellers.

Also there may be increased demand after the floods as companies rebuild business.

Poah, they do, but it's still 240 euros (9840 baht) not even counting my bulky luggage. That seems preposterously expensive - or am I just a spoiled European?

I just paid 2300 RMB for a return flight Bangkok with Thai Airways, booked on their website. I reckon it's not likely getting any cheaper than that, so I guess that's a take it or leave it.

I managed to buy a BKK - KMG for slightly less then 2.000 kuai a while a go so Yereth's price seems okay for the season.

China Eastern flies direct as well, but Thai is a far superior airline. My my hope is that with the new airport more options to Thailand will eventually open up. I used to really appreciate Thai's twice a week direct service to Chiang Mai then they cancelled it in 2009. Now the only direct service to CM is on a little tiny really old regional jet on China Eastern, so I've still just flown Thai and connected in BKK.