Need recommendation for budget lodging near Dublin Airport

You don't say how early your flight is, but you need to allow for a couple of extra hours beforehand for check-in, security, etc. And in Dublin you will go through US Customs before you leave Ireland. Depending on how many flights are leaving for the US at the same time, this can be a lengthy wait. Before you decide on lodging for your last night, make sure that public transportation will get you there early enough from that location. Depending on how early the flight is you might be stuck with taking a taxi.

We Stayed at the Bewley's out by the airport. Super cheap (well under 70USD), very nice, very new. Free shuttle to the airport 24/7. Very close to the rental car returns, and easy to get to from there (between 1-2 miles, maybe 2-3 turns). Lobby is a bit loud, but rooms are quiet.

Hotel is surrounded by horse pastures, where the keep all the racing horses for the horse track, so had some surprisingly lovely views.

We stayed at Bewley's this summer, too. Not much out there by it but the horses, but it's easy to get to the airport, and you can catch buses there into town. We had a room for 4, 2 adults and 2 kids, which cost 89 euro. The rooms were clean and quiet, and had black-out curtains, which were awesome.

The other options we looked at, other hotels or B&B's, required us to take a taxi, which would have added 15-20 euro to the cost of the room. The free shuttle at Bewley's is a great deal.

Thank you all for your replies. We are booked into Ann's of Howth for 2 nights and I'll let you all know how it turns out. We will still have our rental car, and will use it to get to the airport on departure day.