Baxter International Inc. has agreed to pay $64 million to resolve allegations it conspired to drive up the price of certain plasma products used to treat rare diseases. In a written judgment, U.S. District Judge Joan B. Gottschall approved the settlement on the ground that it was a fair resolution of the claims against Deerfield-based Baxter. The settlement brings the total amount of money recovered by the plaintiffs in a class-action lawsuit against Baxter and other biotechnology companies to $128 million. The …