More retailers are providing membership plans and betting that you’ll pay a fee for the privilege of shopping with them. For example, Amazon charges $119 per year for Amazon Prime and has more than 100 million members who make the e-commerce giant their first stop when they go shopping. In exchange for that loyalty, Prime members get lots of benefits, including same-day and free one-day delivery on millions of items, free streaming movies and music, and discounts on groceries at Whole Foods Market. At least a dozen other chain....