OP has no ambition, you can buy rolling stock for scrap value quite easily. If you have an insane amount of labour at your disposal you can do most things for a small heritage railroad by hand. The know-how is not secret arcane knowledge. The main issue is that most countries don't have that many enthusiasts willing to fund those projects. Road subsidies are insanely high but hurr-durr trains are expensive.
I knew a guy who had a vintage passenger car on a little concrete pad on his land. I never asked him how much it cost, but he was an electrical engineer, so it's not like he was rich.