By Leila Abboud and Paul Sandle BARCELONA (Reuters) – Originally derided as a pricey niche product for geeks, tablet computers have become so common that supermarkets are now selling their own brands, pushing out low-cost rivals. And since Apple pioneered the tablet in early 2010, the gadgets now available at the lower end of the market are becoming commodity items that non-technology companies can order from Asian contractors using common components. This opens the door for not only players that can survive on low margins, but also for companies that use hardware as a channel for something else. Tesco in Britain and Carrefour in France are selling their own branded tablets pitched at customers unwilling to pay $400 or more for an Apple or Samsung product. The retailers are not only trying to cash in on booming tablet sales, but also to nudge people to buy everything from films to groceries from their online stores, pushed through their devices, a lesson learned from Amazon and Google.