Benjamines is a fascinating word choice in this song. While it's the Spanish plural of the name Benjamin, in this context, it's a direct reference to "Benjamins" – a common slang term for one hundred-dollar bills, which feature Benjamin Franklin.
This word immediately signals a theme of wealth and success, as the lyrics state, "Los Benjamines empezaron a llover" (The Benjamins started to rain). It's an engaging and somewhat unexpected way to talk about money, making it memorable and enticing for a learner.
The title is the whole joke, once you catch it: "Los Benjamines" are Benjamins, hundred-dollar bills, and this corrido is about them raining down. The singer starts out wanting nothing more than a beat-up car, "Comprarme una Nissansita vieja" [buying myself an old Nissan], and by the time the money shows up, he lists exactly what it bought: new cars, tequila and whiskey, a live band, a gold buckle worn low at the waist ("La super dorada en la cintura" [the big gold one at my waist]).
What gives the song its actual weight is a jail sentence, named once and left alone: "Varios años encerrado" [several years locked up]. That's where he found out who his real friends were, because almost nobody came around while he had nothing: "Dos, tres perros me humillaron" [two or three dogs humiliated me]. It's the same people who wrote him off as a nobody who now watch him from below. He doesn't dwell on any of it; he just says God shut their mouths for him, and gets back to work.