That seems like a lot, of course it depends how many parts are replaced. I get mine serviced in Hong Kong once every couple of decades, whether it needs it or not.
My 'glass' is actually plastic and scratches easily, there is no crystal alternative, I think I am on my fourth 'glass'. My last service was nearly ten years ago and as far as I can remember they changed the glass and the winder. That cost about GBP200/B10,000 equivalent.
The Rolex operation in HK is very big, I believe all servicing is handled in HK. If you happen to pass that way regularly then HK might be a cheaper option than Bangkok, drop it off one trip and pick it up on the next.