JAMIE KELLY Getting Sir Elton John back to Missoula for an encore performance comes with a $75,000 bill. That's how much money John and his agency are requiring the University of Montana to raise for John's AIDS Foundation, which has raised $125 million for AIDS-related work in 55 countries since 1992. The requirement is spelled out in a memorandum of understanding between UM and the Howard Rose Agency, which represents John, who will perform a sold-out show on April 11 at the Adams Center. Two months ago, the Missoulian requested a copy of that memo, but was told it was a “trade secret” and therefore not a public document. Since then, the UM student newspaper - the Montana Kaimin - has obtained the memo and editorially questioned the alleged “secrecy” of the deal.