Try Teach Yourself Irish by Dillon and O Cróinín (see here :
http://www.abebooks.com/servlet/SearchResults?bsi=10&tn=teach+yourself+irish&x=0 &y=0&prevpage=1 ).
It's an old book and you'll find it only as a second-hand book but it's very easy to find on the online bookshops and incredibly cheap. It teaches West Cork Irish (so it's perfect for you).
Be careful, there is a newer Teach Yourself Irish, by Shiels and O Sé, which is completely different and teaches Standard Irish, not Munster one. So make sure you buy the old one by Dillon and O Cróinín.