Amazon.com Inc. has struggled to draw customers to its pricier tablets. So it’s going further down-market. The Seattle online retailer plans to release a $50 tablet with a 6-inch screen, in time for this year’s holidays, according to people familiar with the matter. That would make it one of the least-expensive tablets on the market and half the price of the company’s current Fire HD 6-inch tablet. The move would potentially ...