Spotted a pair of jeans in Wallis in Grafton Street last week - Irish price €55, sterling price £35 (only pair of jeans in the shop with the sterling price left on). That's quite a markup - and I did complain in the shop.
However, you can get around this. Try on the clothes in the shop. Then go to www.wallis.co.uk and buy - you pay normal sterling prices plus £5 delivery to Ireland. There doesn't seem to be a limit on how much is delivered for £5.
It's no wonder that there was nobody in the shop while I was there. The sterling markup is ridiculous. Vote with your feet (by shoping in NI) or with your mouse (by shopping online).