Apartment rental in Thailand will cost you between 3,000 - 10,000 per month. The lower end would be a single apartment room with air-con and fridge. More expensive rents may include two room apartments and a shared swimming pool. Cheaper apartments are available but you may find that the quality is not good. If you are in Thailand to teach, I would not recommend staying in a very low-end apartment. You will need a place where you can relax at the end of a hard days work.