If you have Medicare (age 65 and up), all you need is the "free" part of Medicare (Part A hospital coverage) to be Obamacare-compliant, and thus no penalty.
If you aren't Obamacare-compliant, the percent penalty applies to a "modified" income in excess of the standard deduction and exemptions (approx. $10,000 for an individual).
So as an approximation, it would be 1% of (your dad's adjusted gross income minus $10,000).
I'm not aware that the penalty is capped at the cost of an insurance policy.
Not that you're wrong; I just thought the penalty was uncapped.
If you're right, then Rush has no worries.