WASHINGTON (Reuters) - Democratic U.S. presidential candidate John Edwards on Sunday said that he would raise taxes, chiefly on the wealthy, to pay for expanded healthcare coverage under a plan costing $90 billion to $120 billion a year to be unveiled on Monday. "We'll have to raise taxes. The only way you can pay for a healthcare plan that cost anywhere from $90 to $120 billion is there has to be a revenue source," Edwards said on NBC's Meet the Press news program. The 2004 vice presidential nominee and former North Carolina senator said his plan would "get rid of...