Bought a USB To 3-Pin Cable for S$1.56 and a USB To 4-Pin Cable for S$1.41 from a shop in Shopee called ashionmango.sg. Shipping to Singapore is an additional S$1.00. This is the cheapest USB to 3-Pin/4-Pin cables that I have found.
I like this cable because of the included on and off switch. It is much easier for me to use the switch than plugging in and out the cable.
I will be using it to ventilate the warm air generated by my PC behind my monitor.