I've found the cheapest sharpener for the NYX Jumbo Pencils. Although I don't use them at all I like depotting them for fun. I will probably use them for when I do makeup on other people or I might randomly give them away. I'm not sure yet.
Cheapest sharpener is from meiji.com for 99 cents !(£.63)
It's called Charles Leonard Standard and Jumbo 2-Hole Pencil Sharpener. I was searching for a cheap one for a subscriber of mine who asked me. Shipping is also pretty cheap too depending on where you are but this is the best price that I've found.