The above figures for meals are really dependent on how often you want to eat western food. Typical Thai food will cost $1.50 - $3.00 per meal and western meals will be more expensive. The rental figure in the $1300 column would be for a condo/apartment or a small 2 bedroom house 3 - 5 kilometers outside the city center, further out is even cheaper.
However, if you choose it wisely. You can rent a 1 bedroom apartment in Chiang Rai for as little as $65. For a nicer apartment with a kitchen and living room it could be around $170.
Your utility bill is really largely governed by how often you use the air conditioner and what temperature it is set to, I keep mine on 25c / 75f.
As an example, one of my clients is married with 4 kids. 1 is in primary school, two are in high school and one in university. They live in a medium sized 3 bedroom house which costs $200 per month. They are also paying for a car and their total expenses average about $2,000 per month. Most times they eat at home and the wife either cooks or buys at the market. They go out to eat once a week and a western meal for the 6 of them usually costs about $30.00.
Here's a recent comment on one of my posts from a local expat. "We live very well on a budget of $870 monthly, all including! Only thing missing is a pool in our garden! That's on 2 adults and 2 very spoiled dogs"
Having said all of that, as indicated by the above comment, you could get by on about $900.00 per month but you would have no health insurance and probably no car. You would be using taxis or a motorbike and saving money for emergency medical care which by western comparison is cheap anyway. My husband recently had an ingrown toenail removed; the doctor visit, surgery and medicine costs came to $15.00. My husband also has a complete medical check up every year, this includes, a chest x ray, 12 blood screenings, electro cardio gram, abdominal ultrasound and a physical exam by a doctor. The cost for this is $80.00.