it isn’t.To put the DART charge in context, parking is £35 per day in the long stay car park. I know there are parking packages available, but they're still pretty pricey over a week or more.
its £30 per day, if you’re stupid enough to just turn up. Very few people do this.
I can book now, to arrive in 2 hours time, for £14/day. Or for the car park next to the terminal (a 3 minute walk) for £20/day.