I have no knowledge of how those Part C deals work. My assumption is that the insured pays a monthly premium, and they receive a monthly or yearly subsidy from Medicare. If that is the case, your cost to the government was zip, with the provider losing money on your treatment, and making it up elsewhere.
If my assumption is wrong, I would really appreciate better information. Also, I know that the Part D, prescription drug plans are somewhat subsidized, but again, I don't know by how much, or whether it is per time interval or by individual prescription. Oddly, I'm interested in how much I'm costing.