UN doesn't "say" that. UN pays this allowance to any staff member travelling on assignment to Hua Hin [for instance]. Believe me we didn't feel it was much.
I still use this number when planning holidays, but just as a minimum while I know for sure it is gonna end up 50% to 100% more. And getting worse fast; this march I could still afford a two bedroom suite at Chatrium Riverside, now? just forget it.