Walmart's apparently gearing up to challenge Amazon on its turf and has conjured up a Prime competitor that will begin testing as soon as this summer. According to sources, the company's unlimited two-to-three-day shipping service for online purchases will cost $50, almost half of what Prime costs ($99). Amazon's version comes with add-ons, though, such as free video and music streaming, which Walmart won't be able to offer for now. However, The Information says Walmart is considering adding features to its codename "Tahoe" service. They may include something that involves Vudu, a video streaming service the company owns, as well as same-day grocery delivery, which it already does in five markets. The chain might also partner with other companies for perks meant to entice customers to sign up.