AirBnB has a good number of places in Athlone, which isn't very far. I'm wondering, though, if it would be reasonable to make a one-day bus trip from Galway to Clonmacnoise. That's not very far, either.
And hey, people also take boat tours from Athlone to Clonmacnoise. It's a wonderful place to visit, and the nearby town of Shannonbridge is very nice. You can take the train from Galway to Athlone in an hour, and then take a boat to Clonmacnoise.
The primary boat company seems to be Viking Cruises, which does not run year-round. http://vikingtoursireland.ie/
I'll bet there are other boats.
-Joe-