Zenni Optical takes 20% off sitewide, including lens upgrades, via coupon code "VIPSALE". Shipping adds $4.95. Choose from prescription eyeglasses, sunglasses, goggles, and accessories. Some exclusions may apply. A couple of best bets, with prices after coupon:
Women's Round Eyeglasses for $22.36 (at least $6 off)
Unisex Bodega Eyeglasses for $23.96 (pictured, at least $6 off)