The issue is more that the system is the G3, discontinued model than anything. Those have little value, as they were replaced with a G4 fairly recently. The closest comparison is to the Pegasos, with it's G3, but the Pegasos has more features, so that means need to deduct the missing components from the price....
500 brittish sterling frankly is too much for such a setup. Even $500 USD would be asking too much.
Sorry guy, I wish you luck in pawning that white elephant off on someone. You will need it.