They conflate concepts. You and I would imagine a true professional hitman would charge dearly. Mr. Gottagedridofthebitch, OTOH, has heard, usually from hysterical news outlets, that “among them drug gangs in the 'hood” people get killed for chickenfeed. So it must be plausible to find someone who’d kill on the cheap.
They forget that ***real ***gangbangers/mobsters may have other, nonmonetary, motivations quite their own for killing. Motivations that wouldn’t be at work with some Schmo who just walked into the bar looking to arrage a hit.
There is actually not much evidence that Kuklinski did murder people for the mafia. He certainly did kill some people, but he made up most of his stories about working as a professional hitman. Most people hired by organized crime syndicates to commit murders (at least in the contemporary United States) are not “professional hitmen.” They usually make their primary living doing something else (selling drugs, labor racketeering, being police officers etc) and accept a “contract” to earn some extra cash.
The people who get set up by undercover cops pretending to be hitmen are usually set up by paid informants. Lots of people (usually petty criminals but not always) receive money from the government in exchange for turning in other criminals. “Regular non career criminal types” who are looking for hitmen probably ask people they think would know about such things, such as that guy who sells coke in their favorite bar. The only people who usually take them up on such risky and generally low paying jobs are people who then sell them out to the police.
For someone who was a member of one of those elite forces that you mention, and was in financial difficulty, today’s internet technology would seem to make being a hitman quite easy to accomplish, if that someone is intelligent enough.
I mentioned Kuklinski above, and SecretaryofEvil mentioned that he may have lied about much of his exploits. Whether he did or not, the guy was fucking bonkers (apologize for the language in GQ, but he was fucking bonkers). I saw an interview he did shortly before he died, and suddenly realized where Heath Ledger might have gotten the inspiration for his portrayal of The Joker.