Your maid should know which airline provides cheapest ticket. You can just ask her to arrange it. Normally, they will take the "Oriental Pacific" which has ticket around HK$1,200 for a round trip from HK to Philipines. (not including the airport tax)
Just ask her to give you the receipt, the airline won't cheat you.
p.s. As I know, the ticket just cost ~HK$1,000 for low season.