Third world countries will happily pay thousands of dollars for missiles.
I'm talking about missiles using technology no more sophisticated than what you'd find on a tiny RC plane (which can cost mere cents for China to produce), except with more protection against signal hijacking, and stronger aileron motors since the speeds they're used at are so much higher.
Buying in bulk, the technology for each missile should cost only a few dollars at most since it's just two motors, a very simple circuit board, a radio reciever, and a detonator.
If the third world country uses insanely cheap local labour to produce metal casings and explosives, it could once again be only a few dollars for the casing and warhead of a missile comparable to an RPG (But more like a very powerful grenade, since it's not counting on direct hits)
$10 per missile is a very reasonable estimation of the production cost, assuming they're produced by a single company. Since multiple companies are likely to be involved, it could be a few times higher, but even if you're paying $50 per missile it's a pretty sweet deal if it costs you only a thousand dollars to treat a multi-million dollar fighter jet to crazy amounts of shrapnel.