Update [3/24]: Sold out at Amazon, but still at Staples. 

Amazon has the 12-Pack Pentel Eraser Refills For Mechanical Pencils (White) for $1.89 with free shipping on $25+ or with Prime (extra 5% off for 5+ S&S orders). Same price at Staples. Currently #1 best seller in mechanical pencil eraser refills on Amazon.