Here is a nice article about this subject:
https://medicbilling.wordpress.com/2013/08/22/can-your-practice-discount-self-pay-patients/Here is where it addresses your main question, I have bolded the key part:
"Furthermore, regardless of a practice’s participation status with commercial carriers, if the practice is a Medicare provider,
then it must not discount below the fee charged to Medicare – and most especially, the Medicare allowable, as Medicare law prohibits you from submitting Medicare claims that contain charges substantially in excess of your usual charges. If the discounts consistently dipped below the billed fees, then Medicare would deem that new lower price to be the practice’s standard/customary fee."
So you can go maximum or minimum, but not under minimum for Medicare.
The practices I bill for all have a set self-pay fee schedule, and it is
always the Medicare allowable, it is just easiest that way. To my knowledge, you cannot charge different self-pay amounts to different patients, it has to be the same across the board. If anyone has other info, I hope they chime in.