These figures are based on a single person. As a married couple, the only increase will be for your food costs which may even decrease because most women prefer to cook at home.
The above figures for meals are really dependent on how often you want to eat western food. Typical Thai food will cost $1.00 - $2.00 per meal and western meals will be more like $3.00 to $5.00.
The rental figure in the $1300 column would be for an apartment in Chiang Rai or a small 2 bedroom house 3 - 5 kilometers outside the city center, further out is even cheaper. If you choose wisely. You can rent a 1 bedroom apartment in Chiang Rai for as little as $60 - $90 per month. For a nicer apartment with a kitchen and living room it could be around $150.
Your utility bill is really largely governed by how often you use the air conditioner and what temperature it is set to, most people keep theirs 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 for 2 adults and 2 very spoiled dogs".
In my opinion, living on $870.00 per month would be challenging but I do know another client who does all his own cooking and eats out once per week and he lives on $1000 per month. The man is single and lives in a very nice city centre condo where he pays rent of $437 and walks everywhere except for once a week when he takes a taxi to the supermarket.
Having said all of that, you could get by on about $1000.00 per month but you would have no health insurance and probably no car. You would be using taxis or a small 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 tests, ECG, abdominal ultrasound and a physical exam by a doctor. The cost: $80.00. My husband is also an insulin dependant diabetic and the cost of his medicine (Metformin, Diamicron and Insulin), is $70.00 per month.