Guys that have been collecting longer than I have probably remember what a 59/66 was going for when they were first imported. Back when Russian models flooded the market here and were cheap, no one had seen a 59/66 with grenade launcher. They were imported well used and in limited numbers.
I don't remember how much they went for exactly, maybe $1000 or so but the people who bought them kicked themselves hard when mint ones came in years later at around $200.
These rifles were still being cranked out well into the late 80s and some have speculated even later than that. I'm thinking we haven't seen the end of them.