How much money is required to enter ireland?

I'm going to Ireland from the 13th of july to the 5th of october. I don't want to get turned around at the airport because I don't have enough money. Does anyone really know how much I need, or if they will even give me the boot if I don't have enough? I'm staying with my fiance who's parents have posted me a letter saying that I won't be expected to pay for anything as I will be a guest in their home. Is that good enough?