Amazon has for Prime Members: PowerA Nintendo Switch Joy-Con Comfort Grip for both Red and Black on sale for $7.49. Shipping is free for Prime member or with $25+ purchase.
Camel indicate this is lowest price past 12 months.
Black : https://www.amazon.com/gp/product/B01MS7YUA7/
Red : https://www.amazon.com/gp/product/B01NBVACKX/