In my opinion, having a Masters Degree makes no difference in what you may be allowed to charge.  Even in a related field.  

Basically it is supply and demand.  I do know many private tutors, all foreigners and native speakers, and the charge where I am at runs from 70 to 100 Rmb per hour, up to 6 students per class sitting.  You must see with other foreigners within the city you live at what they charge and can get away with.

But basically, what you can charge will be what your student will be willing to pay, and how good you are at teaching English, and how interesting you make each class.

Wages really depend on your location.  Tutors in first tier cities can charge at least 200-400 an hour per person.  In second tier cities it's more like 100-200.  In third tier cities, you wont find many people willing pay that much--they have all moved to better cities. 

I've met tons of people who'd like to study English from me, but they balk at paying 100 an hour.  This is a reality for many Chinese where the average pay is around 2k a month.  Your masters will help you with HR at a company or university, but private students are much more concerned about other factors, like your personality, price, and ability to travel to their house.