Different guys got different deals.
I know that in '65 for instance, there were spare parts for the AFX contract racers on basically a "what do you need?" basis.
That could include a spare body in white (happened with the Melrose Missile), and my AFX buddy tells stories of visiting S&M and seeing so many Hemis that they'd walk over them to reach the far end.
What the money was, I'd need to call; but '68 was a different period, and my source was off contract then.
Of course, there was also the Supercar Clinic program, which IIRC paid, but was as we know very limited.