The only likely benefit a rail stop would have, would be a negligible increase in passengers from the Coleraine area. The vast majority of passengers travelling to LDY either get there off their own steam, or use taxis.
Public transport to the airport is more or less nonexistent, and before there's a debate about a rail stop, surely a dedicated, hourly bus link between the airport and Derry City centre should be the priority? As it stands, the very infrequent buses that do serve the airport, do so at such times as to be pointless (none arrive in time for the early flights, and the last one of the day is around 4.30pm).
So, a couple of hundred grand on a rail halt, or on developing a dedicated bus service?