This comes from Alan LeMay’s novel The Searchers (you may have seen the film, starring John Wayne), where he’s writing about trade between Euro-Americans and Native Americans in the late 19th century.
And they took a great quantity of sheet-iron arrowheads, the most sure-fire merchandise ever taken onto the plains. These were made in New England, and cost the traders seven cents a dozen. As few as six of them wold sometimes fetch a buffalo robe worth two and a half to four dollars.
In addition to arbitrage, the quote reveals how trade makes both sides better off and the role of technology in making products that are both better and cheaper.
Although the novel isn’t actually about economics, you should still give it a read. I don’t read “cowboy stories,” (tried to read a Zane Grey book once, or maybe it was Louis L’Amour, but just couldn’t hack it), but The Searchers is not a cowboy story. Like True Grit, it only uses the frontier west as its setting for a very human story of love, tragedy, and and epic search for revenge and redemption.