@ralord82276An old dead tree novel, by Cordwainer Smith. "NORSTRILLIA". IIRC, the MC gains access to an old (and somewhat illegal) military computer and uses it to play the commodities market. Becomes massively wealthy.
Obvious expansion of that idea is using a computer, or a new program, or MC is a statistical genius, magic,etc. Stock market, commodities market, money markets. Bets on sports.
Another old story is probably more along your line. "The Cosmic Computer" by James Schmitz. A poor community on a frontier world scrapes up enough cash to send MC to Earth to research the location of a supposed abandoned sector HQ that they believe to be on their world. It was supposedly built for the final campaign during the past interstellar war. Then, the war went a different direction.
Mc doesn't find that info, but develops a plan to bootstrap the economy. However, since everyone is expecting the base, he has to deceive them, while still getting their cooperation.