Perhaps the vet said "Proliferative bowel disease" and in your stress you
misunderstood her.  It is a disease that could match the symptoms you
described.  I would think that the vet would realize that 6 months of age
is very young to have insulinoma, and would have checked for other, more
obvious signs rather than rely on a simple blood glucose test.  Also $800
to $1000 is quite high for a pancreatic operation; at least around these
parts of the US.
 
I'm glad your regular vet got back in time to prevent a costly and possibly
dangerous operation on your sick ferret.
 
Dick B.
[Posted in FML issue 2429]