You're welcome

Another school with a good reputation for repeats/ selection of subjects is St. Tiernans in Sandyford. It is a community school, but as far as I know they allow their repeats to wear their civvies rather than a uniform. It sounds like you are looking for something that will treat you more as an adult than a schoolchild. You could also look at some of Cork's/Dublin's VEC colleges where they also do PLC courses. This might be a cheaper option but still 'feel' like college?
I would 2nd the opinion that coming to Dublin and paying for cost of living will negate any saving you make on fees, unless you have digs sorted out.
If you are worried about not getting the points to do your course of choice, then maybe consider a PLC in Cork and use the points on that to get into your course next year, unless of course it's medicine or similar you are trying to get!
Best of luck with your search.