Here we go again.... I think the best answer is, "If you have to ask...."
Rates for TOP NOTCH schools here (as you asked!) would easily be 300K-500K per kid per year, not including any possible "sign on donations" which smoothed the entrance process (because entrance can be quite competitive at a couple of these places). Let's say, easily a million baht the first year, 300-500K thereafter.
Not a cheap proposition.