It is not going to be "cheap" but years ago I had Circutron make me up a set of
boards to run subway cars.
It was for two trains, but the idea was this, the train starts either stage
right ot stage left in a tunnel. When power is applied the train moves out and
enters the station, where it stops, waits a few seconds and starts again, it
then enters the tunnel at the othe side of layout, a turnout is thrown and it
repeats the run in the opposite direction......... add nauseum and it was also
configured to run a second train, but that one has to be operated.
I have the boards somewhere, and their setup notes, but never got the time to
bild the dang thing.