We already know how to cheaply and efficiently build rail, rail cars, huge systems for pulling and releasing the cars (they are called engines and overhead electrification :) and in fact you can pick up a lot of the materials used for less than half the cost of new. Dozens of km of land are damn near free in places in the southwest US where you can also dump lots of solar panels. Lithium may eventually be cheaper, but not within the next decade it won't.