Newchic offers this Rear View Blind Spot Mirror 2-Pack for $6.50. Coupon code "SPOT30" cuts it to $4.55. With free shipping, that's around a buck under what third-party sellers charge for similar via Amazon and eBay. They're 3mm thick and feature adhesive backs. Deal ends May 14.

Note: This item ships from China and may take two to six weeks to arrive.