If it was me looking at it,
Most of the value would be determined,
In the condition of the Toolbox.
Then over-all condition of the bed.
If he has a key to the toolbox buy it
As far a price goes,
From your description,
The toolbox is worth as much as the bed.
Depending on condition of both of course.
Ask what he wants for it,
Then offer $200.oo or so less,
Unless you like the first offer.