I paid a lot less than the agent's quotation in the end as I didn't need her to do much. I did more or less the same thing as what Jessieywl did, and my helpers arrived within 6-7 weeks.
If you potential helper has never worked in HK before, the HK immigration department, after reviewing your application, will return the green contracts back to you and ask you to get them "verified" by the Phillipines consulate, who in turn will ask you to get them stamped by their "approved" agent first. And of course, you'll need to pay some money for the agent's stamp!
Note that your helper will need to pay some fees for the seminar, body check and stuff in the Philippines, and this may be quite hefty for her but it's entirely up to you whether you are prepared to reimburse her or not. (But read the green contract, there are basic items in which you HAVE TO REIMBURSE her regardless.)
You can always call up the Phillippines consulate to ask for more details regarding agents etc. The staff there are really helpful.
Hope this helps. Good Luck!