Good question about the fees ! I'd say to check the Help page on fees specific to Ireland, because eBay charges slightly differently in each country (I suspect on a "what can we get away with here ?" basis).

But I don't think sending offers attracts extra fees, if anything you'll end up paying slightly less on the Final Value Fee. The big advantage is that you're proactively approaching someone who is already interested in the item and could be nudged into buying. What I'd suggest is send the offer at a price halfway between the initial price and the lowest you'd take because it goes some room to negotiate. But as always - experiment !