$400 a pop

John GrishamのThe Racketeerを読んでいます。米国に本当にあるのかどうかは知りませんが、Rule 35の適用で釈放された主人公は名前をMaxに変え、顔も整形して別人としての生活を始めました。
We spend the next two days running errands and getting Max firmly established. I write my first check to a car-leasing agency and drive away in a used Audi A4 convertible, mine for the next twelve months at $400 a pop and fully insured. Now that I’m mobile, and now that Pat and I are getting on each other’s nerves, he starts talking about his exit. I’m ready for the independence and he’s ready to go home.
$400の後に付いている "a pop" の意味が分からないので辞書を見ます。
・Collins Dictionary: (informal) each: 30 million shares at 7 dollars a pop
・Merriam-Webster's Online Dictionary: for each one: apiece: The tickets are selling at $50 a pop.