Three's SIM only plan is €15 per month until the end of the year. Comes with unlimited data, no fixed contract, calls and 3Plus rewards - if you will use the rewards this is worth while. They regularly have good offers from likes of Just Eat, Elverys, Eason. I've saved plenty of € using it. If you wont use the offers however Virgin's €5 for 5 months deal is better value at the moment.