Some schools will do it here it is just more paperwork I believe, but you have to have your TL( Teacher's Licence) too to do it. P.S Tax number as well.
Depends where you are? It can be just as cheap to go to Cambodia. As someone or people suggested "do it yourself" it is quite away from Kanchanaburi town. When I went few years ago now I hired a motorbike ( 200Baht + 100 Baht petrol ) but I use to live there so I know how to get there but I wouldn't recommend it the road can be quite tricky in places.