Link to the Youtube video (it's right at the beginning of the video when the reporter says that)

Transcript:

James Rhein is out on three hundred dollars bail after being charged with criminal mischief. He tells me he doesn’t think this is that big of a deal. And he adds that his wife is "fine with it."

Why does she say three hundred dollar bail with an "s" on the end of dollar? Isn't that grammatically wrong? We don't say, for example, he is a five years old boy; we say, he is a five year old boy. What is really going on here grammatically?
I, actually, was told that many Americans do say three hundred dollars bail, but no explanation was offered.