I am unemployed with no insurance. my knee is very painful. what are my options for low cost?

If your income is low, you should visit a county hospital ER. If your income is not low, you should deal with an orthopedist's office for a discount with cash pay. My office usually offered a 50% discount for a cash paid visit.

A local community clinic that offers a sliding scale fee for non insured individual, many times around medical schools if living in a city with a medical school. The visit itself might not be very expensive, treatment and possible tests will add up to the cost.