Use the dollar sign in all instances that demand numerical specificity. Only spell out "dollars" in casual or abstract cases. For example, "The book cost $4, but dollars are flowing overseas."
Use a singular verb for specific amounts. For example, "He said $500,000 is what they want." The verb "is" is used instead of "are."
Use the dollar sign and up to two decimal places for amounts of more than $1 million. Do not use hyphens. For example, "He is worth $4.35 million. He is worth exactly $4,351,242. He proposed a $300 billion budget."