Formal:
* Deux cents dollars: This is the most literal translation and is perfectly acceptable in formal settings.
Informal:
* Deux piastres: "Piastres" is a slang term for dollars, often used in informal conversations.
* Deux billets de cent: This literally translates to "two hundred-dollar bills" and is a more specific way to say it.
Ultimately, the best way to say it depends on your audience and the context of the conversation.