Our wedding guests gave a fairly uniform 200 euro/couple, with the exception of a few aunts/uncles who gave more, and two couples where we only knew one of the couple attending who gave 150. I was surprised by how exactly the same the cash gifts were, but then that's what we would give too so I guess its the 'norm.'
Would disagree with the idea that getting married down the country necessarily saves the couple money - all the nice, country house type venues are very expensive. We went with a city centre wedding in the end on the grounds that the majority of our guests would come from Dublin and there was no point them having to pay accommodation but we did feel bad for the 40% of guests travelling to Dublin who had to find a hotel - after extensive ringing around and trying to negotiate group discounts, the cheapest we could get was 185/night for a couple, and that was not anywhere especially fancy. Thankfully lots sorted themselves out with air bnb etc, but I was shocked by how expensive a hotel in the city centre on a Saturday is.