you need a non-immigrant b visa — and if u dont want to leave every 90 days - you need an extension based on work - (need to fulfil the requirements) - your lawyer/accountant can you give exact details. you dont need to be offic. resident.
yeah that is the Samui price - you can extend it every 3 months like this and not need to border run.( it might me price from the school , as I got that offer for a friend as well and was wondering)
apply and get back next business day — its not a working visa - its non immigrant b - with this visa he cant work - he need it to apply for a work permit.