How long is a piece of string? 🤷♀️
Are your DC likely to be eligible for a grant? There's a pretty wide sliding scale for eligibility and even the smallest grant that pays half the student "contribution" will help a lot.
And even if you don't live near a 3rd level institution, what's "near"? It's pretty common for students to commute over an hour to college, esp of private bus operators drop direct to the college gates. I know several students that have done 90 minute commutes each way for a couple of years at least, as it was cheaper than renting near the college.
So if you could add up a best case / cheapest and worst case / most expensive scenario, then you could budget to save enough to at least cover the cheapest version (dearest version is a bonus). Put it in the best interest-bearing account you can find (not necessarily a credit union) to keep pace with inflation.
E.g. cheapest scenario might be living at home, maybe eligible for grant to cover some part of fees or even maintenance, giving 50 euro per week for lunches, beer, etc, plus bus/train travel card for commuting. Student also gets a job during the summer and actually saves the money to help see them through the year.
Dearest scenario might be renting in Dublin (eek!) at 750 per month, no grant at all, giving 70-100 euro per week (or more...) for food, beer, and buses, and maybe extra to cover travel home for the weekend. Student doesn't get a summer job and/or doesn't save anything to help during the year.