The Hyogo International Association in Kobe offers evening Japanese classes for foreign residents for a nominal price of 2,000 yen per semester: Hyogo International Association. (Find the English PDF at the middle of the page.) Sign-up is on a quarterly basis and first-come first-served.
There are a number of other places in Hyogo Prefecture that offer Japanese classes on a weekly or monthly basis. The best place to get information about these is the Hyogo Nihongo Volunteer Network that has a list of most of the available Japanese classes in Hyogo.
In Tajima, cheap and weekly lessons are offered by Nihongo Toyooka AIUEO
In addition, some JETs are permitted to take some time during the summer to study Japanese in an intensive summer program. Some of the programs that have been recommended in the past by Hyogo JETs are: