Hi,
lots of schools do evening classes, including German classes.
They tend to stop for the summer, so you'd prob have to wait until september.
I did German night classes in the community school in Dun Laoghaire years ago, and found it good.
The only bad thing, is they they tend to have 3 levels (beginner, intermediate and advanced).
Of course to start with you are a beginner, but once it's finished, its difficult to know what to do next - you are prob not advanced enough for intermediate, and there's no point in doing the beginners one again.
Thats why places like the Goethe Inst may be worth the extra money - they have loads of levels, so its easier for continuous learning.
(However if you just want the basics for a holiday abroad etc, the other school night classes would be fine).
Ragazza.