board of investors , they will approve your LTR visa and if you meet all the requirements they will take care of the further action with immigration for your visa. They will help you during the entire process . And that all for free, you only pay the visa fee directly to immigration or if you are abroad you have to pay directly to the embassy. You can google on boi LTR.
You can get all the information and help for free from BOI; look at their website; the total costs are 50.000thb to pay directly to immigration office or to the embassy (there might be a difference in this amount when abroad). It’s a waiste of money to pay more; if you meet the requirements it’s a piece of cake.
You better ask your immigration office; then you know as well the exact amount what it will cost, should’ve be about 5700thb for extension and multiple entry