That price seems about right to me. I had a quote of $600 to clean my Breitling B2 last year (price from Breitling).

There is a very good watch repair shop right next to Emporium on Suk Soi 24. They are about 60 meters up the soi from Sukhumvit on the right hand side. Easy to get to using the BTS (Phrom Phong).