I have probably bought and sold more mixtes than any other forum member because there is strong demand for them in both the northeast and around Ann Arbor. The sell for more than the equivalent men's diamond frame and step thru models.

The Beltway is a high priced bike market, like NYC. Nonetheless, for $250, the Peugeot you are looking at should be near perfect, with matching tires, new cables, and the old Simplex Delrin derailleurs replaced (dark plastic). As they are prone to crack or wear out. very good examples of Peugeot mixtes can bring north of $300.

The Lotus below is a nicer mixte mostly because it has alloy rims.
Women's Mixte Lotus city bike