i would recommend 4-player match play. you'll maximize the point values that way. with 8-12 players, you only need 3 machines if you want everyone playing at once, or you could get by with 1 with more time for socializing.
depending on people's schedules, i recommend meeting weekly or every two weeks. make the season long enough to get 100% tgp, but not much longer, or you'll leave points on the table.
as far as the cost, i'd say make it whatever people are comfortable spending. i've seen anything from $0-30