Officially booked our tickets the other week. Philly -> Paris -> Dublin for $376/person. Not bad at all.
I also think I've found a hotel for us.
The Ardmore Hotel. Booking through Travelocity it's only $48/night! It works out to be half of the cost of the self-catered apartment. And I don't think we'll spend the other half on food, since neither of us are big eaters. I ran the search through other cheap hotel sites, and none of them compare to Travelocity prices. Glad I searched it on a whim!
The hotel has a bus stop right outside, and it's close to the connoly train station, so we'll be able to get pretty much anywhere else!
Will a taxi be easy to find at the airport? The hotel is 2 miles away from the airport, but I think it's too far for my mom to walk (especially with bags!) and the bus you have to go into town and transfer to another bus, so I'd rather just stick us in a cab if possible.