When I had mine done, last September, it was £63.
In other words, the same as the DVLA Group 2 medical, for which I was charged separately.
I believe the main reason for the variation in charges, and some of them being high, is the fact that GPs were just confronted with potential NPPL people asking for the signature - without having been informed officially about it. My GP sounded particularly incensed that there had been no guidance through the medical officialdom.
Still its a fraction of the CAA medical through an AME - which I had done in March.