Michigan runs one of the nation's largest and most costly prison systems, a $2 billion-a-year expense that is crowding out other spending priorities at a rate many officials fear the state can no longer afford. . . The problem is reaching a crisis. . . It could exceed capacity within two months, said Chief Deputy Corrections Director Dennis Schrantz, unless lawmakers approve stop-gap measures, such as doubling the number of inmates in the state boot camp program. . . The Corrections Department already devours 20 cents of every tax dollar in the state's general fund and employs nearly one in every three state government workers, compared with 9 percent of the work force 25 years ago.