The numbers sound correct. The only real question is whether there was lower fare bucket availability for that J fare. But, it seems unlikely to me that a phone agent would sell into J when there was a lower fare basis available unless the passenger expressly asked for it.
As to the tickets being expensive in the first place, that is simply a function of close-in booking on a route where your situation is entirely normal. E.g., people either booking or changing at close to the last minute.