those same fans from actual name brands like coolmaster,antec and so on are only 5$ on newegg sometimes free shipping. or go to computer expos and get them even cheaper. if i had to pay 20 per fan for a computer build id be broke on fans.

and a 4" fan is actually based off mm which is 120mm fan

here ya go Have fun ordering.
http://www.newegg.com/Product/Produc...40%20-%20%2410