It doesn't cost much to do a little preliminary transportation engineering.

I'd get out a map of existing RoWs that still exist, either as rail lines, or trails, or unmaintained tracks. This is the most expensive part, that was done long ago. It's hundreds of millions of dollars sitting there if you can rehab an existing RoW.

Next, it'd be expensive to run a single Amtrak train once a day to, say, Montreal. And the capacity would get saturated very quickly, like the recent service to Burlington. And it's not something you could plan a day trip around, and you're competing with high-speed air. So you'd almost immediately be more expensive, slower, and more difficult to plan a trip around than high-speed air. Then when demand plateaus... the bonds come due.

Rather than doing that, look at your population centers, attractions, and current vehicle traffic volumes and start asking questions.

Are there enough people that want to take a light rail into downtown Burlington from the surrounding suburbs? How many people would take a light-rail to Montpelier if it ran 10 times a day? How many people would be skiing at Stowe if it was possible to get there without parking their car for a few hours between the resort and Waterbury? There are a lot of places in Vermont that will basically become impossible to drive to with just a very moderate increase in vehicle traffic. That makes light rail somewhat imperative, unless most people are just priced out of going anywhere.