Inshore jackets: Why do the prices vary so much?
First off, the waterproof level. Jackets at the lower end of the spectrum will often only have a waterproof coating on the fabric as opposed to a membrane. Jackets with membranes offer a higher level of waterproofing and are more durable. These membranes are designed to keep water droplets out, but allow perspiration to escape, so will be more breathable and waterproof than a coated fabric..
Jackets designed for mild weather often have an exposed zip which is not waterproof. As you go up through the price range, you find ‘storm flaps’ (a flap that covers the zip) or even waterproof zips.
Jackets designed for more inclement weather will incorporate comfort features such as fleece lined hand warmer pockets (location varies between models) and high, fleece lined collars, and ‘drop seat’ salopettes for women. The jacket may have an insulated lining for additional warmth, and will have the addition of reflective patches for visibility.