VSAT cost effective service for low usage yacht SEA

hi i am looking for VSAT airtime with an intelllian v60 with up to a 16wattBUC for southeast asia only .

the client only has minimal requirements say 256/128 and he only uses the yacht a few weeks a year, do you have any of the following options.

1.pay just monthly as needed?
2.Pay as you go
3.fixed amount of DATA per year fora yearly fee with top up if needed?