If you need details about cost of living in Chiang Mai in Thailand then you should be referring to the right websites that specialize in these things as they would know better given that they may have spent time researching all information before presenting them to the public.
This makes it important for you to refer to multiple websites to get a good idea, or to put it this way, a ‘better idea’ on what the cost of living in Chiang Mai would be given that different websites may be basing their conclusions upon different factors and criteria. It is therefore difficult to rely upon a single website for all types of information pertaining to Chiang Mai province given that it is quite a large region with different areas and hence the chances of a single website specializing in a certain area would be higher.
And the problem with such a situation is that the area that they may be specializing in may not be where you would be about to travel. So as soon as you have decided that you might be moving to Chiang Mai it would be a good idea to look for cost-of-living information for the province so you can make your mind up on the right area that you could perhaps take residence in.