It's amazing to hear that you will be performing in Dublin with your students!
First of all, let me share these industry tips
for school trips in Ireland that you might find useful. You could perhaps consider splitting your group into two, which would be more feasible in order to find accommodation for 30 people. I'd also suggest looking for hostels outside of the city center to lower the bill if that's feasible for you. Our accommodation search engine
will give you an overview of what's available in Dublin.
Have you asked the venue where the choir will perform for any leads?