When someone asks me where is the best place to stay in Chiang Mai on a budget? I always recommend Fu Residence. I stayed in these apartments for a few months last year and IMO, you will not find better value for money in Chiang Mai. You can walk in right off the street and they usually have apartments available. If you stay for 6 months or more, you can get them for 7,000 THB a month, £150 or $190.
And best of all this is not a single room condo. This is 4 separate rooms with two separate air con units. Pretty hard to beat! Situated just 5 minutes from the Old City, close to the night market and the nightlife. The location is hard to beat also. If you want to know more about Fu you can click the link to their Facebook page below. Or click the link to the Google map.