Price is not always the key but the nicer ones do tend to cost a bit more but I had a peruse of the Celtic Whiskey Shop's website and the following is what I could come up with. All below 100Euro.
Personally I would not bother with Midleton Very Rare and although it is a nice whiskey for me it is too much of an easy drinking whiskey and not especially interesting and a bit obvious.
http://www.celticwhiskeyshop.com/ They have a Flat rate delivery of €7.95 anywhere on the island of Ireland no matter what you buy so even 2 bottles could be an idea.
The Celtic Whiskey Shop in Dawson Street in Dublin currently has ...
Green Spot Chateau Léoville Barton @ €69.99 quite limited and excellent by all means.
Redbreast 15yo @ €97.00 a cracking whiskey and a constant favourite amonst whiskey drinkers
Powers John's Lane Reserve 12 Year Old @ €63.99 this is also a cracker and very much a favourite of mine.
Tyrconnell Madeira Finish @ 75.99 another very good whiskey but is bottom choice of my list.
From what else I saw online I was not over hit by anything of outstanding quality. The only one I can't comment on is the Celtic Whiskey Shop - Celtic Cask Ceathair Deag (14) and @ €135 the most expensive of the list but I have no clue of this and how it tastes. others to consider also would be Jameson Gold or Jameson 18yo which are usually avialable widely.
If your buying one of the cheaper ones above you might consider adding second in a nice presentation box which you can easily do yourself. I would suggest with maybe 2 glencairn glasses as these are the glasses he can use to explore the whiskey. Tumblers are more for a relaxing drink by the fire.
Teeling Single Malt @ €52.99 great value as it is really admired.
Writers Tears Copper Pot @ €44.99 another middle end whiskey.
And if you go for the Redbreast 15yo you could get him this book
A Glass Apart: Irish Single Pot Still Whiskey by Fionann O'Connor a wonderful book about Irish potstill whiskey.
If Dublin based you could buy him a membership to the Irish Whiskey Society.
I'm sure others will pop in here and give other ideas so remember it is all about personal taste and if you are unsure just go with your own gut feeling.
I'm sure no matter what you get he will be delighted
Best of luck on the big day