I don't have a copy of the letter, but have heard reliably that it went out to friends recently. It was described as a somewhat rambling letter that eventually got around to the point that he'd definitely be running in 2014. It noted that there'd been rumors that he would not run, that he might run for governor, that he might once have been interested in the presidency of the University of Arkansas. He said those rumors weren't true, that his family was happy at their home in Little Rock and that he looked forward to another race.
UPDATE: Here's the Pryor letter.