Yes, cash gifts are the norm in Ireland.
DH is Irish, I am English & we got married (many years ago) in England, with a good mix of Irish & English guests.
I committed a bit of faux pas as far as MIL was concerned in having a gift list. We had items varying from a very modest £10 up to around £100, but we didn't ask for cash at all. Unbeknown to me, gift lists were not the done thing in Ireland, at least not at that time. You don't have a list, and while some guests will give you a gift, most will give you cash. I was
at the generous cash amounts DH's relatives gave us because I wasn't expecting it, and very grateful of course.
The contrast was interesting between the English guests and the Irish guests. English guests either chose a gift from the list or gave us cash, but smaller amounts than the Irish guests.
In your situation OP, I'd just give what you can afford - don't be pressured into giving more. Around €50 would be absolutely fine, I'm sure, especially as you've had to pay for travel costs etc.