@Cha****
Oh, not it's not that it's that hard or anything it's that you paid 200USD for that visa :O and I thought you'd wanna get your money's worth.
You can certainly bank the 400K for the requisite time required in a thai bank account, get the required documentation and go apply for a yearly extension. It's not that hard and is actually pretty straight forward. You certainly can do it yourself and don't need an 'agent' to help you at all with it.