As you've pointed out, pay in different faculty differs from one another due to different budget. As a rough gauge, admin work in Biz fac usually pay better than say Sci or Eng Fac.

But personally I've yet to see anyone I know wishing to work in NUS; it's like the end of your career in my opinion. Sure work-life balance is superb, but promotions, increments, bonus are worse than civil service, and hardly anything interesting/exciting nor will you learn anything useful.