Reply #3: It's not actually terribly expensive

[KatyMan]

All in all, I would guess it would cost less than $250, depending on various fees for documents you might need. You need to prove that you're related to your grandfather (or mother), so you need:

grandparent's birth certificate (whichever it is, g/mother or g/father)
grandparent's marriage certificate
grandparent's death certificate, if applicable
your mother's (or father's whichever it is) birth certificate
your mother's (again, or father's) marriage certificate
your birth certificate.

Those documents, along with forms from the Irish government, are all you need. If you have a lot of your docs, it shouldn't cost too much. I had to get new copies of everything except my birth cert, so it took some time and a bit of money, and digging to find out the correct records offices (I was living out of the state where I and the rest of my family were born). I was able to get a copy of my grandfather's birth certificate from Donegal, and he was born in 1885!

I'd say go for it, because the Irish government is tightening laws on citizenship (for example, if you're a citizen by descent, it used to be you had to be married 3 years for your spouse to be able to apply <3 years after you attained citizenship>, but now you and your spouse have to live in Ireland for 3 years).

That's about all I have to say for now, just a general overview, but glad to answer any other questions (at least, ones I know the answer to!)