Amazon.com has Classic Accessories 73422 Veranda Kettle-Style Barbecue Grill Cover (fits Weber Original Kettle 18" and 22", Original Kettle Premium 22", Weber Gold Series 18.5" and 22.5" and Silver Series 18.5" and 22.5" models) for $10.40 with 3-year warranty.
Per CCC, lowest price ever. Free shipping with Prime or on orders over $25.