It's a one-off payment if the channels you want to watch are broadcast Free-To-Air (FTA).
If the channels you want are encrypted, you need to buy a viewing card from the provider and pay a subscription. Your hardware must be compatible with the card. Some FTA tuners have no slot for any card, some cards only work in certain tuners. You should also check if the provider of the encrytped channels is prepared to sell to an Irish address.
LyngSat provides details of what satellites can be recieved where and which channels are encrypted.
I can receive 'Thor' here in Dublin, but most channels require a card. HotBird and Astra contain most of the FTA channels many people watch.