One of the things you have to love about the Irish is that they have many rules, and usually just the exception to fit your needs. An example is that anyone getting married in Ireland has to give notification in person, by appointment, at a registrar office at least three months in advance. But if you are not living in Ireland, you can ask permission by mail. If permission is granted, you still have to present yourself at the registrar office in person, but that can wait for as long as until five days before the marriage.
Official information about getting married in Ireland can be found at the website of the Irish General Register Office.
Among the documents you will be required to produce are birth certificates. If they were not issued in Ireland they must have an apostille stamp attached.
Same sex marriages are not permitted in Ireland, but the Civil Partnership and Certain Rights and Obligations of Cohabitants Act of 2010 allows same-sex civil partnerships, whose requirements are similar to those of marriage.
The fee for marriage and civil partnership certificates is 20 euros, or about $26. But the notification fee recently rose to 200 euros or about $266.