I've been lucky enough to have purchased large and small post & pre war collections at great prices over the years. Kept what I wanted and sold off the rest, usually at train shows, at a profit. Those profits are what I've used to support my addiction.
One of my most interesting purchases was about 15 years ago. I went to have my new SUV pinstriped and, at that time, my plate said "TOYTRNS". The pinstriper asked if I like trains, I said I did, and he brought me into the back room of his shop. There was a huge (and I mean huge - around the size of 3 ping pong tables) table of trains from 3 generations: his grandfather's Standard gauge, his father's pre-war Flyer O gauge and his post war Lionels.
He asked me if I would be interested in buying them and threw out a $1,000 price. I jumped on the deal. I went to the bank and then to grocery and liquor stores for every box I could find to carry them. Filled up my SUV with the back seat folded down. The stacked boxes covered the back window and the front passenger seat.
Mrs. 'Ski went nuts when she saw me carrying box after box into the basement.
I kept some of the Standard gauge, cherry picked the Lionels and sold the rest over a year or so (after cleaning, lubing and repairing) making about a $2,000 profit. That bought a lot of trains for Warrenville and paid for another collection purchase a year or so later, a lot of that was worked on and then sold at a profit too.
This luck happened to me only one other time since. All of these times it was dumb luck that I was in the right place at the right time.