Sorry, Kzinga.  Seems like either your math is lacking, or your statement is incomplete.
If we all pay $50 per month into a system like Medicare, then each of us can expect about $50 of medical services per month.  That would just about cover check-ups, vaccinations, and preventative care.  Any significant illness or injury would be way out of budget.  Given that we spend $3.2 trillion on health care per year in the US, that works out to about $10,000 per person per year, or $830 per month.  Even if you can reduce costs, without also reducing the amount and quality of care, we each will need at least $500 per month.
On the other hand, if you meant to say that medicare for all should cost "you" $50 per month, then you must mean it should cost others much more.