Late to the party here. But do you have some sort of a preference on type of trains? I mean, do you want models of trains you see running on the rails today, or maybe trains that you saw as a kid, or something else?
My first advice is to not be so worried about doing things "right" that you don't enjoy it. Never in the history of model railroading has something been put together that hasn't been changed, and then changed again, etc. Model railroads don't happen they evolved with the owners interests and experience.
As for cost, it can be as expensive or cheap as one wants to go. I just blew $600 for a
single steam locomotive, while if one watches the sales one can find them for $100. Like this one -
https://www.trainworld.com/manufact...omotive-dcc-sound-on-board-boston-maine-1360/ With the Bachmann brand one has to be a bit careful. They make some pretty good stuff (like this 2-6-0 as MHinLA said above), but they also make a lot of toy train low quality stuff.
There is lots of good information already in this thread. There is also never only one way to do something.