Who is the cheapest to register .ie domains I hear you say? Say it! Say it! Anyway, there is a good blog article on this over here. I charge around €60 over at my web design and hosting company Red Tomato.
I can bring the price down if I'm hosting or designing aswell.
The problem for me is that I am not a reseller, I am a reseller of a reseller. Check out how you become a reseller. They make you jump through a lot of hoops but I think it is the way to go so watch this space.