We came up with our fee schedule based on a precentage of what medicare will reimburse since that is public knowledge. We then offer a 30% discount to anyone who pays on the day of service. This is legal because we offer it to everyone, including the insurance companies but since they will never be able to do this, it's only the cash pay patients that benefit.
You can also legally write off part or all of a bill later down the road, but you must first charge everyone the same and the person will have to tell you they can't pay it at which time you "negotiate" what they can pay, if anything at all.
There is a way to legally charge people different prices based on income but it's so tedious that I'm not going to attempt it. There are a few clinics in town that do that but you have to verify tax forms, paystubs, etc..yuck.
