Arizona's plan to turn over state prisons to private companies in exchange for a $100 million upfront payment is having trouble getting off the drawing board.

The plan is behind schedule and private prison operators aren't showing much, if any, interest. And an official who worked on it says that the $100 million figure was based on hope, not certainty.

The privatization effort is required under a law enacted as lawmakers struggled to close a huge budget shortfall. It directs the state to award a "concession" to one or more private companies to run an unspecified number of prisons for $100 million.

It emerged as Republican lawmakers looked for alternatives to Gov. Jan Brewer's proposed temporary sales tax increase.