As a half-Thai, half-Farang child, my father spent 150,000 THB per semester for me to attend an international school. There are two semesters per year. Our family lived in Chiang Mai, where owning a car is essential without one, it’s difficult to get around. If you're considering renting, I would recommend renting a house. Prices vary depending on the location, generally ranging from 10,000 to 40,000 THB per month.
As a child in international schools, I honestly didn’t enjoy the experience at all. Many of the students were wealthy Thai kids who bullied me. I never hated school as much as I did when I attended an international school. Making friends often depended on whether you had the latest iPhones, iPads, or drove a car during your high school years. I ended up dropping out and studying for the GED instead, which eventually led me to enroll in an international university in Chiang Mai. But even there, I still hated it. Studying was difficult not because of the academics, but because of the constant bullying and materialistic attitudes among the students.
So if you’re thinking about moving to Thailand, especially to Chiang Mai or the northern region, think carefully. Many people there are extremely materialistic and only look into your pockets when it comes to making friends.
Yes, there’s also the issue of the smoky season, and to be honest, there aren’t many places to buy Western food. There’s Rimping Market and Central Festival—at the bottom floor, you can find some Western groceries—but overall, Chiang Mai has become quite expensive.
If you want to know the names of the schools I attended in Chiang Mai, feel free to DM me. I would strongly advise avoiding them. I can recommend a few international schools, but to be honest, they're not much better than the others.
I hope you will make the right decisions for you and your family.