Amazon lists the Staedtler White Vinyl Erasers for 65 cents. Probably some shipping added unless you have enough other things to get free shipping. I have never found a better eraser for pencil or graphite.
When using them in a classroom, I take take them out of the sleeve and write ART DEPT or my name (if they are mine) on both sides of each one with a Sharpie marker.
Many schools have a place where students can buy pencils. What if quality erasers were available for students to purchase from the school? Students would use them in other classes as well.