Store coupons may get some shoppers to buy targeted items, but adwoman Janice Dupuy knew a lot of people refuse to take the trouble. Her idea: a silver plastic card that can be used in lieu of paper coupons throughout the year. Express Savings Inc., in Houston, aims to get 500 retailers to join its network by year's end, paying fees of $195 and up. Next year's goal: to sell 600,000 cards to shoppers -- at $25 each. -- Leslie Brokaw