Accor has weekly private sale where you can score great deals (oftentimes it is 25%-30% off). I can't post the link because I am new member to the FT forum (need at least 5 posts). You can google though.

Sofitel Hua Hin is on this week's list but looks like the nearest day you can book the sale price is Sep 3rd (last week you can book in July for a sale price)