Dear Zinc,
If you are single,then you cant sponsor her.
Regarding the basic salary,it depends on the nationality of the helper (600-1,500 QAR).
You can only sort this out once you are in Qatar.
Ask help from a colleague who has family status and qualified to sponsor one for you, or hire someone from here, who has already a resident visa or sponsored by her husband.
I think if the price is right, they will go for it.

Good Luck.