It's becoming something of a joke along the Maine-Canada border. So many busloads of retired people crisscross the line looking for affordable drugs that the roadside stands should advertise, "Lobsters. Blueberries. Lipitor. Coumalin." Except, of course, that such a market in prescription drugs would be illegal. These senior long-distance shopping strees fall in a legal gray zone. But as long as people cross the border with prescriptions from a physician and have them filled for no more than a three-month supply for personal use, customs and other federal officials leave them alone. The trip might be tiring, but people can save an average of 60 percent on the cost of their prescription drugs. For some, that's the difference between taking the drugs or doing without. "The last bus trip I was on six months ago had 25 seniors," says Chellie Pingree, former Maine state senator and now president of Common Cause. "Those 25 people saved $19.000 on their supplies of drugs." Pingree sponsored Maine RX, which authorizes a discounted price on drugs for Maine residents who lack insurance coverage. The law was challenged by drug companies but recently upheld by the U. S. Supreme Court. It hasn't yet taken effect. Figuring out ways to spend less on prescription drugs has become a multifaceted national movement of consumers, largely senior citizens. The prescription drug bill in America is $160 billion annually, and people over 65 fill five times as many prescriptions as working Americans on average. "But they do it on health benefits that are half as good and on incomes that are half as large," says Richard Evans, senior analyst at Sanford C. Bernstein, an investment research firm. What's more, seniors account for 20 percent of the voting public. It's little wonder that the May 19 Supreme Court ruling got the attention of drug manufacturers and politicians across the country. The often-over-looked state of 1.3 million tucked in the northeast corner of the country became David to the pharmaceutical industry's Goliath. The face-off began three years ago when state legislators like Pingree began questioning why Maine's elderly population had to take all those bus trips.