not really. Extensions are 1900 each and they depend on your next court date. These extensions are usually several months apart (excluding mediation stages) so the visa covers your next court date + about a week or so after it. You pay on the spot at immigration and you can extend depending on how long your court case takes (normally 1-5 years unless settled).
File a lawsuit against these scammers. then you can get a litigation visa for as long as the case lasts. I've done this for a civil case before and it works fine. Yours would be a criminal one so you and your son may very well get a couple of years visa
I don't know how it's going to be now but you can give it a shot. Bangkok Bank the branch opposite the McDonald's on Soi Buakhao. Try the young lad if he is still there.