That's great you enjoy your hobby. I would love a model railway, I think they look amazing and the details to the trains and objects looks incredible! I wish I had the space to do my own.
Track is cheaply obtained secondhand. People say not to buy secondhand track but it can be obtained so cheap that if it does not work it can be repaired, especially if one knows how to solder onto PCB.
Rolling stock... The main costs of scratchbuilding are the wheels and couplings. One can make ones own couplings, and plenty of people upgrade from plastic to metal wheels so plastic wheels can be obtained at cheap prices.
