If you are doing it in a railyard why not install a powerful wifi hotspot in the yard and use that as an intermediary?
Or maybe you could use an Arduino with high-power nRF24L01+ mounted on a tower in the yard as the intermediary between two other Arduinos with nRF24 transceivers.
I don't believe in throwing money at a problem but it is equally ridiculous to be a cheapskate.
...R
PS. You should have told us up front that the train will be stationary and in a yard. Several folks have wasted time on comments that assumed the train is moving.