Hi Harry. Prices for those in my area (South Florida) vary quite a bit. I'd say its worth between $100 and $200, although I've seen them for sale for as little as $50 and as much as $500.
In my area, SoCal, I have a friend that has been offering to GIVE one away, for years. So far, no takers. So, I'm thinking the lower end of the price range. If it's been out in the weather, and has water in it, almost nothing. The brakes are worth something, if they are usable.
I have never paid over $100 for the rear.axel, torque tube, etc. Check the "web" at the front of the banjo for stamped numbers that will tell you the gear ratio, and always pull the wheel hubs to check the condition of the surfaces of the ends of the housing for the usual spalling to see if it is usuable. I have been given several axles from rodders who are building a car.
$100 bucks is a fair price as most sellers get tired of stepping over it in their garage.
Plus, you don't know its internal condition. Was it always stored inside out of the weather?
If not..$50.