When one is too broke to afford a cigarette, and thus can't afford to solicit sex from a prostitute, they take a drag from a prostitutes's cigarette, usually for the low price of only a nickel; The cheapest known way to satisfy a nicotine craving.
Hooker: "Hey buddy, you lookin' for a good time?"
Mel Gibson: "Well ya, but I can't afford that. You got a cigarette? I could go for a hooker smoke."
Hooker: "It'll cost ya a nickel."