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.

USB to 3-Pin/4-Pin Cables
USB to 3-Pin/4-Pin Cables

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.

USB to 3-Pin/4-Pin Cables - Switch
USB to 3-Pin/4-Pin Cables – Switch
USB to 3-Pin/4-Pin Cables - USB End
USB to 3-Pin/4-Pin Cables – USB End
USB to 3-Pin Cable - 3-Pin End
USB to 3-Pin Cable – 3-Pin End
USB to 4-Pin Cable - 4-Pin End
USB to 4-Pin Cable – 4-Pin End

I have a spare Arctic P12 PWM PST Fan since the value pack comes with five fans. My PC case, Lian-Li TU150, only supports up to four fans.

USB to 4-Pin Cable - 4-Pin End Connected To Fan
USB to 4-Pin Cable – 4-Pin End Connected To Fan
USB to 4-Pin Cable - 4-Pin End Connected To Fan - Powered On
USB to 4-Pin Cable – 4-Pin End Connected To Fan – Powered On

I will be using it to ventilate the warm air generated by my PC behind my monitor.

USB to 4-Pin Cable - 4-Pin End Connected To Fan - Ventilation
USB to 4-Pin Cable – 4-Pin End Connected To Fan – Ventilation