Good idea, Angelin, let's share data. Here's my impression from my maid and from comparing notes with a few friends. I should also mention that a porteña friend says she never employs mucamas who have worked for foreigners because we spoil them and they expect to be overpaid!
The hourly rate depends on the number of hours worked and whether it's en blanco or en negro.
For full-time work en blanco (with obra social, social security, paid holidays, vacations, and sick leave), an hourly rate of 18 - 25 seems to be fairly standard.
At the other extreme, a few hours' work each week en negro should cost 25 - 30 pesos an hour, and most mucamas will ask for a few pesos viatico to cover travel costs.
Now, foristas, what are you paying your mucamas?