in my opinion, its simple to convert to electric, almost plug and play (and might well be)
the price will vary alot, depends how much you can get the parts. I got all the parts i needed for £50. All depends what you can get the motors and regulators for. And you may need new door cards, definatly new handles.
You could convert to electric mirrors at the same time. its pointless me detailing what you got to do. its all wrote out in the maintenance section. Go have a glance.