Matalan is a club - you'll need to join up before you buy anything. I think you can do this at the cash desk, just be aware you have to do it. It used to cost £1stg, I've no idea if that's still the case. I've just googled it and found "http://en.wikipedia.org/wiki/Matalan". It sounds like they might prefer you to join up but not insist on it anymore....
I travel reasonably regularly to Craigavon from Dublin West, you'd be doing well to do it in 1hr 10 mins. It might be a bit quicker now that the M1 is complete around Newry (maps.google.com gives me 1hr 40mins). Maybe it would be 1hr 10 mins if you could stay at 120kmph the entire way . . .