Some of the cheapest options for buying prescription glasses online include Zenni Optical, Eyebuydirect, Goggles4U, Liingo Eyewear, Diff Eyewear, Vint and York and Warby Parker. GlassesUSA.com is one of the cheapest places to buy designer prescription eyeglasses from brands like Ray-Ban, Oakley, Prada and Persol.