Always use a dollar symbol followed by digits to represent a dollar figure: the candy cost $2; a $485 dollar ticket

For numbers in the thousands, use commas: a $50,000 bonus

For numbers in the millions, billions, etc., use digits followed by the multiplier: a six-year, $117 million contract

For cents, use digits followed by cents written out: a 50 cent piece; 5 cents

As part of an expression, simply write out the figure: looks like a million bucks; just my two cents; penny for your thoughts; five-and-dime