English instructed High Schools by Kadikoy? (Istanbul)

Hello everyone.

My family is looking to join me here in Istanbul this summer and am looking for any recommendation for English instructed High Schools for my son (Doesn't know any Turkish). We live in Kadikoy and need the school to be located in the Asian side. I found a few schools like "American High School" in Uskudar but I can't afford their tuitions. They're asking 15 to 30K dollars a year.

Can anyone recommend or advise on a school that is affordable?

Thank you!