Ah, how many M16s can you get for $1 million?
My guess would be between 1,000 and 3,000 M16s. The low number assumes M16 goes for 1K a pop; the high number assumes $333 a weapon. The latter number is probably what the civilian market would bear; the former assumes the usual price gouging for Govt contracts.
M-16s are cheap, but grunts to shoot them aren't. This is an area denial weapon, not an individual one. It would be analogous to a crew served weapon.