I'd go with an adgroup for each county (even geo targeted to each county...doesn't work so well in Ireland).
In each ad group pile in the list of car makes.
mazda
honda
honda civic
VW
VW Golf
VW Passat
Then your ad can be:
{keyword:Cars} For Sale Cork
Get the best priced {keyWord:Cars} In Cork
Our {keyWord:Cars} List is Updated Daily!
www.mycar.ie/{keyWord:Cars}
****************
VW Passat For Sale Cork
Get the best priced VW Passat In Cork
Our VW Passat List is Updated Daily!
www.mycar.ie/VW-Passat
(I am aware the char limits are a little off, but you get the picture)
Hope that helps.