We looked into doing this a couple of times a few years back. One has to be careful not to "short haul" your business. Perhaps some of the public would like a shorter trip, but they are still willing to pony up the full fare for a day's ride. By offering a shorter and cheaper alternative, how much full fare revenue will be lost to the cheaper trip?
In order to make it attractive you need to price it with a minumum of a 2/3 price of the regular trip. Unfortunately, 90% of the expense of running the railroad is incurred between Chama and Cumbres. It takes coal, maintainance and manpower to get up that mountain. It costs very little to go from Cumbres to Osier and back. In order for a short trip to pay for itself, the fare would have to be nearly the same as the full trip.
Then, we would have to find a crew for it....
We did offer a shorter train/bus trip from Antonito/Cumbres and back. GBart did offer a bus to Cumbres and return by train in the afternoon. I think it did fairly well considering it wasn't really publicized. It was intended primarily for the after lunch walk up business.
Knowing that 1/2 the travelling public tends to forget to pack a very important item - namely their BRAIN - making sure people get in the correct car at Cumbres so that they could return to Chama would be an unending nightmare. Getting the straight through passengers to trade trains at Osier is bad enough.