I got stung at Waterford last year for 5 euros. The only other place I've had to pay in cash was Vancouver.
I think this is a most hateful way of collecting the money - much better to do it in with the purchase of the flight (nearly said 'ticket', there, but we don't have those any more, do we!)
So, Waterford is close to the sea (but I wouldn't call it particularly mountainous, just a bit hilly).
Digressing slightly, a most excellent place, small & friendly, they even let us hold an aerobatic competition in the overhead every year. Do visit Dunmore East if you're ever Waterford-bound.
The OddOne