Thank you very much turfit.
I think I just turned off the tree to make my tests in more controlled environment, you can turn them on again.
I use the power of the vehicles to extrapolate their capacity. If that capacity is far from the one that I aimed, then the price will go up, but it will also impact down the running cost. So specially if you find a long section of loco with the same speed, the first ones will be more expensive but very cheap to run, the next will have their price go down and the running cost go up and near the top, the price will go up again and the running cost will drop again. I think the explanation for this is in this thread that was the only solution I found.
The locos are intentionally that cheap. If it cost more, it would be a strong motivation to always fill the locos at maximum capacity. IE. 7-8 tiles long (or whatever I set). The cheapest one should have around 4 tiles long, but you should find locos that are best at any length. And you should be able to play a lot more with different lenght as well as running mixed-goods trains much more often in this pak. True it doesn't matter much, but it still matter. Having small locos with only 1-2 wagons is an option.
It's supposed to be 100 unit per month. I'm unsure why you end up with 300... However, you can compare the prices of the freight to do the math. Half the price = double the traffic. It's quite high for the pax.
And yes, I considered a little part of the trip on unupgraded road going side way. To be exact, I used 1.5 in my equation.But I also increase the running cost by 10% each step. So yeah, we end up around 1.85 or so
I will be happy to jump to 2.2.0 as soon as I can find the source code for it. And have a bit more time forward.