Its not just budget. Its risk. There is an expectation of safety that is on a civilian transit system that is not expected in the military. You can't just MacGyver and hack parts together on a public transit system like you can in the military. There are wayyyyyy stricter standards etc for a public transit system, and I know what you will reply with "the military has strict standards too" and, they do, but nothing near what is required for the TTC and GO.
People join the military with an expected understanding that there is risks involved with such a job. People do not go on a transit system expecting the same level of risk.
It isn't MacGyvered when it is made using the blueprints. The problem is, the ships we had just a few years ago, some of them were older than 40 years old.