What is the required process for a father seeking sole custody of 3 minor children while the mother is incarcerated?

The mother of the 3 minor children has been on ongoing probation for Endangering the Welfare of a Child - 2nd Degree (Intoxication/BAC) - Vehicular since 04/2o11. After six violations of probation (scram bracelet), she was sentenced to 180 days of incarceration. The divorce, finalized in April 2012, details that the mother is not to drink or have the children in an environment in which drinking takes place. The mother has been in violation of the divorce degree (drinking clause) various times prior to being arrested, in addition to numerous other violations of the divorce degree. She owes back child support since April, in other words, has not provided child support for the children since the divorce was finalized. She was jobless for 3 months prior to jail and upon being released will be without a car or a place of live. The father is seeking sole custody of the children and is considering representing himself in court. The financial burdens he has endured over the last year and a half prevent him from being able to pay several thousand more in lawyer fees to be represented to modify the custody arrangement. What is the best approach for this father to seek custody modification- in a fairly inexpensive, but effective way?