SNES / NES dust protectors

I was looking around and the prices for them seem a bit janky~

NES were going for about 1-2$ a pieces and SNES closer to 4-5$ That seems a bit crazy to me seeing that every single one of these cartridges that was sold came with one >.>

Does anyone know good source to pick them up in bulk?

 

I see a lot of them on Ebay as a bundle for pretty cheap.

 

I remember seeing an online template you could print off so you could create your own NES sleeves.