In the strictest terms. A student visa is for study only, at the institution that provided that visa. Any other use of the visa is illegal. This includes part time work, paid or unpaid.
The Chinese authorities are now clamping down on people misusing the visas.

You may have heard different things from different people about what you can and cannot do with a student visa. But the word can is a selective word. e.g. you can work on a student visa, you can also murder, rape, and run drugs. But all of these are also illegal.

Alas, not so easy.
If you pay high salaries the money has to come from somewhere. The parents will not pay the higher prices. They would expect better teachers for the same price, this is natural considering everything. Market forces then create an impenetrable wall.

The university pay is governed by bodies outside of the university, and this is public money. I don't see that going up real soon.
Teachers can try to control the supply by refusing to accept work for less than a certain amount, but as long as there is some kid in the US who is loved up with the idea of coming to China there are more people willing to take the place, who are less/non experienced. This is a negative spiral. That is where we are at right now.

@jen

Perhaps your views are those of a woman.
Not of men who have trawled for sex.

Our views are not 'silly', or 'naive'. They are outside of you world view.

Has the entrance been moved out to near the town? This would help the restaurants run by people from the town and other parts of the local economy, not run by park management.

You would need Chinese language to tell them what you want and to negotiate membership.
Sorry, I have no idea how much.