You know, if I had millions lying around I’d want to build or buy a small <10km line in rural buttfuck Saskatchewan and ride train cars around, just for myself and letting people that made it here use it for fun. I haven’t tried estimating how much that would cost.
Have a look at the West Coast Express, opened in 1995 from Vancouver BC to 43 miles out at an estimated cost of 40 to 80 million Canadian dollars, equivalent to 53.4 to 106.8 million of today’s USD. There were musings of it as far back as 1971, but it sounds like design started sometime after 1981 and construction started in 1994, finishing late 1995.
The price tag would include 5 engines and 5 sets of bilevel railcars, leasing tracks for CP and BNSF, building a handful of turnouts and sidings to hold the trains when out of service, build or contracting wash and maintenance facilities, maybe some small track and signalling upgrades along the route, and station facilities in 7 places.
Another example is the Rail Runner Express in New Mexico that runs 96.5 miles from Santa Fe to Albuquerque. The NM Governor Richardson announced it in August 2003. Construction began in October 2005. The first portion of service began in July 2006 and the full line went into service by December 2008. The cost to build the line was about 285 million USD total equivalent to about 438 million USD today. A operational deficit of 10 to 20 million USD annually was reported and criticized, but roads and bridges of that length cost as much to maintain anyway.