Are you going to do it yourself or go thru maid agency? For my prev maid, I got it done thru agency for about $450, incl passport renewal. If doing it yourself, then go to MOM's website:
Ministry of Manpower | WP Online for Employers of Foreign Domestic Workers
This is extracted from the website:
Once your eRenewal Request is approved, the Work Permit will usually be renewed for 2 years. However it is subjected to the validity of the worker's Travel Document/Passport (1 month before the expiry of the Travel Document/Passport); validity of the Security Bond/ Personal Accident Insurance expiry date (2 months before the expiry of the Security Bond/Personal Accident Insurance), maximum period of employment and other criteria whichever is shorter. Hence do ensure the Travel Document/Passport and/or the Security Bond's/Personal Accident Insurance's validity are/is extended or renewed before eRenew. For Security Bond and Personal Accident Insurance, also do ensure that the latest information is updated into the WPOL before requesting eRenewal. (Personal Accident Insurance applies only for foreign domestic worker)
Is your an Indon or Pina? If Indon, the passport renewal will be more expensive and troublesome.