There's no point in spending 5e unless the relevant documentation has been made available to the Irish GRO and can be searched.
If you search now and are told there is no record, it may well be that's because the records haven't yet been compiled/collated and a different result may be obtained in a couple of months' time.
It also occurs to me that it could be the case that a UK citizen marrying in Eire may be required to have banns published at their nearest RO which is why I've suggested that checking with your local Registry Office should be your first port of call.
The system in Ireland may be similar to here in that notification of intent to marry is given to a church/registry office and sent to the GRO ostensibly for checks to be made as to whether the parties are free to marry. Given the number of cases of bigamy that occur annually, it's not a foolproof system.
But the point is that a notification of intentionto marry is subject to alteration. As an intended marriage may not take place, reliabilty can only be placed on obtaining a copy of the actual marriage certificate which, as I've said, may take some time before it is made availabe to the general public.
Check your local Registry Office first and give it a couple of weeks before you call Dublin and specifically ask how long it takes for them to have a record of a marriage that may have taken place perhaps in a parish church miles from anywhere.