As someone who lives in Ireland I would suggest ORD-DUB-ORD, I'd be very VERY suprised if the upgrade didn't clear, infact I'm surprised there's no availability now, I've never seen ORD-DUB-ORD full in J.
Then take AerArann to Galway. It might be an idea to try to use a travel agent and get an interline ticket or else leave plenty of time between flights on the return, Galway airport does suffer delays from time to time with fog.
Taking the bus is possible, there is a privatly run bus service from Dublin Airport to Galway citylink.ie, taking the public bus is too much hassle, getting a bus into the city and then another back to Galway could take 5 or 6 hours. Same with the train, you have to get into the city and the trains are not very frequent.
If you don't mind the smaller planes Aer Arann is the way to go.