shops are free to charge what they want even if a euro price is displayed.
Easons are the main distributors of magazines here and they will give a rrp to newsagents.
the calculation from sterling to euro is based on the following
uk cover price + 10% distribution charge
x current 6 month set exchange rate of 1.18
+ 13.5% vat
So for every £1 uk cover price, the euro price will be €1.48 incl. VAT (No vat on mags in UK)
£2 = €2.96
£3 = €4.44
£3.90 = €5.77
Though I do know of a newsagent in Monasterevin that adds their own extra 10% to EVERY magazine, even the Irish ones - needless to say, I don't buy anything there!