My family has a flight from DUB to the US, and I've been trying to find a cheap way to get from Paris (where we're staying) to Dublin. Aer Lingus has much better pricing on my travel dates into Belfast vs. Dublin. I was shocked at the cost of a one-way one-day car rental ($300+ USD), so I'm wondering if there is a convenient bus or train service between the 2 airports (Belfast to Dublin). Thanks!