I would imagine that these weapons are much cheaper to buy in Mexico that here in the States.
I wonder why no mention of Mexican ports where container ships dock and offload are never mentioned. Are we supposed to believe that the federales have a security stranglehold on those despite the rest of the country being out of control?
Actually, they are much more expensive if they are "bought" but - not an issue. Most of these weapons are "freely" given. Heavy arms are provided to the narco gangs by corrupt officials - both military and civilian. In exchange, these officials get drug money and provide protection to the drug gangs. In turn, the drug gangs provide "protection" to the corrupt officials.
A couple of hundred thousand American dollars is coffee money when you are involved in a drug trade to make hundreds of millions of dollars.