There's no longer is a boiler grant. There is a €700
Heating control upgrade grant. An 18kW condenser boiler will probably cost between €2k and €2.5k depending on brand and excluding fancy heating controls (which the grant would cover). A BER and a bit of form filling should secure the grant but you have to put the controls in.
https://www.localheroes.ie/ should give you and idea of what you need and what it could cost.
I got an 18kW Worcester Bosch before Christmas. I didn't bother with heating controls or grant.