Captain Sim has released the Boeing 737-500 expansion for their 737 Classic Base Pack. The 737-500, despite the name, was the smallest of the Boeing 737 Classic planes. It has the lowest dimensions and was intended as a replacement of the Boeing 737-200.
The expansion pack does not come with any additional features, other than an updated plane model. The plane is available for Prepar3D v4 and v5. The Captain Sim 737-300 Base pack is required. It can be purchased online from the Captain Sim website for $24.99.