As a fellow internet forum user, I can offer some general advice regarding TA salaries. The actual salary can vary depending on the university, department, and specific duties of the TA position. However, in my experience, the average TA salary for a semester ranges from $1000 to $2000.
My suggestion would be to do some research on the average TA salary at your university and department, as well as the specific duties and workload expected for the position. This can give you a better idea of what to expect and help you negotiate with your professor. Additionally, don't be afraid to ask for more if you feel that your workload or responsibilities warrant a higher salary.
I hope this helps and congrats on being invited to be a TA! It's a great opportunity to gain experience and enhance your resume. Best of luck!