At ComboInk, buy one refurbished HP 920XL-Compatible High Yield Inkjet Cartridge 4-Pack for $25.96 and get a second one for free via coupon code "DN920HP". (Add two 4-packs to your cart, then apply the coupon.) Shipping adds $3.99, or spend over $50 to qualify for free shipping. Each 4-pack features one each of black, cyan, magenta, and yellow ink cartridges. A 1-year ComboInk warranty applies. Deal ends May 31.