mrs tide likes the Chalachol Salon de BKK at the Emporium. It's a shopping mall on Sukhumvit Soi 24 (BTS station: Phrom Phong). She does not speak Thai but language has not been a problem - English (and Japanese) spoken.
I've been there for haircuts as well as Chalachol's other place on Siam Square (it's called Q - big minimalist white billboard with the word "Q" in red - 3 floors of shop space!) - I think I paid US$15 for a haircut IIRC. Nice place - never been disappointed.
I have also tried Chalachol's place at the Robinson Ratchada - this was the cheapest but Ratchada's a little out of the way.