囡囡要我每月給她12000元做我女朋友

I don't know the ususal rate but my friend has a "privatized lunch box" and it costs him $10,000 ymb a month and he has to pay for the rent of the apt in CP. He spends about 3-4 days a week in CP, so I think it is worth while for him.
I have a sauna girl told me that she had been a " girl friend" for a Taiwanese and she got $10,000 a month and when the guy left her, he paid her extra 30K. I guess this guy is generous.
Put it this way, if you spend the same amount for sauna, you could go 17-20 times a month!!! It all depends on how you preceive the value. If you only plan to DO her for few times only, then forget it. If you budget is too tight or you won't able to spend enough time with her, also, forget it too.