Aside: Derby Blades On Amazon by mantic59 Posted on July 3, 2012 If you like Derby blades, Amazon has a 100 blade box on sale for about $7. Yes, that’s $0.07 per blade. Derby Extra Double Edge Razor Blades, 100 Count About mantic59 Shave tutor and sharpologist. View all posts by mantic59 → This entry was posted in Shaving. Bookmark the permalink.