[Vautrin]

Actually I just checked. The line is a whooping 6.0 miles. The expenses are mainly caused by the fact that a lot of buildings are already in place there, and that as a consequence highly expensive tunnel drilling techniques need to be used. And quite a bit of the track is above the ground, so the estimate would be that it costs easily 350-600 million euros to lay track a mile of track under the surface.

But for smaller towns busses and the like will do. You can even look into metro (as they use regular roads), for towns between 200.000 and 1 million people in them.

As I imagine most cities, the problem is that work is mostly concentrated in a few grids. Which means you have to have in that grid a highly expensive parking options (which space could otherwise be used as space for businesses). So the main problem would be in that specific grid.

In most cases a metro supported with busses will do.

London is bad, but imagine what it would be without the tube.