It sounds like the problem could be 1 of those 3 things, but since they're not sure which one, they're covering them all. That computer is definitely the most expensive part. Since the defroster also doesn't work, I bet there's nothing wrong with the wiper motor. A computer problem or a sensor (switch) feeding the computer sounds more likely.
Did they tell you that they tested all of those things independently? If not, and if you're comfortable with taking the back door apart, carefully removing the plastic panels, then it would be worth it to do your own diagnosis. For $10 for one day, you could access
Toyota TIS to look at/download the relevant parts of the Service Manual. The manual is usually pretty good about telling you how to test components, especially switches and motors.