(again with the no edit feature :P)
Turns out there are a lot more variables in play than just those. You need to keep industrial growth from goods deliveries and such into account, as well as demand for more/longer trains.
I tried generated a map with two roughly evenly sized cities within a reasonable train distance along the river, which took a few tries. Ran both scenarios for about ten years (I forgot to take yearly budgets for specific numbers), and “reverse” bus lines are not entirely useless, but probably more suited for a “five years in” addition to catch the last people for the train line.
Train income (Two trains with 3 cars each – was too little for the later years because of a bit of AI growth)
~400-700K (The pass loop wasn’t 100% consistent as to be expected)
Bus lines (Larger Town)
50-60K and 40-50K for each direction (Income was a bit higher with just one line, but the second line caught up in a few years)
Bus Lines (Smaller Town – It had about 3 stops less and was much more compact. Harder to get people take the lines)
20-35K and 15-20K for each direction.