"I called AARP today to check. The had an alternate plan to the one they're providing which costs nothing, but sticks you with a modest copay for a primary care physician's visit and a much stiffer copay for each visit to a specialist."
AARP is a reputable organization but even then it's a good idea to check AARP-approved medigap offers.
A few years ago I chose one of them. It cost me $84 per month. And then I had some minor surgery; Medicare of course did not cover it all, leaving me with a couple of hundred dollars to pay.