My comment only relates to wheelchair.
I was wondering about this for a walker. Page 40 in the current Medicare and You talks about Durable Medical Equipment. DME is subject to the 20% coinsurance for Part B. I think caveats being, it has to be prescribed as medically necessary and sold by a provider enrolled in Medicare. I did not see any indication of $20 co-pay.
It was a rhetorical question I already know there is no copay for those things alone