Thailands winter is Dec/Jan/Feb which is basically the high season for tourism (it's hot but not stupidly hot). So it's more expensive than other times of the year but still cheap by rest of the world standards.

This channel has some pretty decent vids on the subject

https://www.youtube.com/channel/UCmnpMr4Md5CgZ5MdlghTYqA/vid...

Bear in mind though that Chiang Mai is more of a rural town than major city, you might find yourself preferring Bangkok.