Walmart offers the Greenworks 20-Foot String Trimmer Line Replacement Spool 3-Pack for $19.47. Opt for in-store pickup to drop it to $6.71 $6.19. (Amazon charges a few cents more the same with orders of $25 or more.) That's the lowest price we could find by $2. It fits Greenworks 21062, 21602, 21222, and 21132 string trimmers.