We have at least 12-week leagues.
Each week EVERY player pays an extra £3.00 league fee on top of the normal tourney buy-in. These £3's are collected and used to payout league prizes at the end of the league. So if the average turnout is 40 players then there is 40 * 12 * 3 in the league fund (or £1440). This is chopped in a similar fashion to a tournament prize split., e.g 50% for 1st, 30% for 2nd etc based on the league points they earned during the league.
The final 9 players will all get points (but not all necessarily money - i.e. if only 28 players we only pay money to top 6, but all 9 will still get points) - 1st gets 10, 2nd 8, 3rd 7 down to 9 who gets 1 point.
Sometimes we may have a sponsor who may offer a big tourney seat as a prize, e.g. EPT Copenhagen. We still collect the £3's and in this case the winner of the league gets the seat and the league func collected paid to 2nd place onwards. The number of places is largely determined by the amount of money collected. Also, these special leagues are also longer - more like 26-week leagues.