If you plan to keep the car, invest in a code scanner. You can find them online for as little as $38.50 shipped. Would save you a lot of time and money not having to brought to a shop before you can at least see what the code is. Once you know what codes they pulled, you'd have a better idea of what to check. It sounds like they are taking the flat-rate approach of changing parts. What are the chances both modules failed at the same time? Even if it was one of the other, that is a lot of cash just to found out it is a sensor or short etc.
