"I was sold to this house for the price of six won"
For half a second I thought she was sold for what was basically six pennies, as I'm more familiar with the post-independence won.
Since the first chapter is set in 1926, and Soo-a says she's been the lady's servant for ten years, this would have been in the brief period when the puppet Korean Empire had a new currency reform in 1902 issuing gold won matched to the international gold standard. While still technically its own sovereign state, Japanese authorities closed down the Joseon bureau responsible for the production of specie and struck all the coins that would actually be issued at their own mints in Osaka, and the specifications are more or less identical to the Japanese Yen. So, going by the international exchange rate of the Yen in the 1900s, at least we're talking dollars rather than pennies.
In other words Soo-a was sold to the Yeo household for a pathetic three U.S. dollars.