How much does a 1972 e pluribus unum one dollar coin cost?

There is no such thing as an e pluribus unum dollar coin, what you are referring to is an Esienhower dollar. To buy a circulated one, you can pay about $1.50 at a coin shop, or occasionally banks may get one or two in and you can get it for face value. It is a common coin and an uncirculated example should run you only $3-4 at the most (assuming you want the most common die variety).