Are you setting up a website in opposition to Clans of Ireland Ltd.?
No, not in opposition to but in addition to. I checked out www.theclansofireland.ie but I was only able to find the dates and family name of upcoming clan gatherings. They seem to have a broad range of service to provide to their paying members. So I thought it would be a good idea to set up a free service focusing on clan gatherings only.

Does it cost anything to advertise an event?
No. This is a free service