It depends. You have to assemble a lot of documents. If you don't have official copies already, you have to pay for those, usually $10 to $20 each. The cost of registering my foreign birth was a few hundred dollars. Once I have that in hand, I have to apply for a passport. Since the papers are things like birth and marriage certificates, I paid to send them express certified, which I will also do with the passport application. When you add everything up, it'll be between $500 and $1,000. It can be a lot more if you don't have an Irish born parent or grandparent. This is a good explanation of the process. https://expertvagabond.com/dual-citizenship-ireland/