Last year I went to O'Connell Street holding a sign saying "Ticket Wanted". I was shocked at the way some people tried to sell me forged tickets. One ticket said "Croke Park, Upper Level", with no mention of who was playing, what the occasion was, the date, or anything else.
Anyway to answer your question, a fella offered me a genuine ticket for 120 euro. Its face value was eight euro. If I go to this year's All-Ireland, I will take the same approach. I really don't know how else to get a ticket.