Maynooth to Mayo (Castlebar/Westport)

Yup, train is the best bet, there's student deals for intercity fares on irishrail aswell, I know it's 20 euro return to Sligo so might be something the same for Mayo:)

Had a big long post written imparting all of my public transport knowledge that is now negated by the fact that there's a new timetable coming into effect as of October 7, boourns although yay for no more 6 hour long ridiculous gap between buses! Oh, and the Castlebar buses take hours so your best bet would be jumping off a 22 bus in Swinford and getting collected if that's a possibility. Bus Eireann is also cheaper than private operators AFAIK and cheaper again if bought online. They also have been known to throw up €10 return journeys online during the year which is awesome.