I don't ever recall seeing PL/M compilers advertised by anyone back in the day. I have a feeling that the few that existed were offered at "meet our sales guy at the golf course" pricing.
PL/M was developed by Gary Kildall for Intel, and the only compilers I've used ran under Intel's ISIS family of operating systems, originally on Intel Intellec MDS hardware, and only much later under first-party ISIS emulation on MS-DOS.
AFAIK, Intel never marketed its first-party development systems to hobbyists, so you're probably in the ballpark with "golf course" pricing.
AFAIK, Intel never marketed its first-party development systems to hobbyists, so you're probably in the ballpark with "golf course" pricing.