As I am licensed in Florida and Vermont, I cannot offer you specific advice as to Oregon law. However, generally, it would appear that the third-party contractor is primarily responsible for your damages. It is unclear if that is the insurance carrier with whom you are trying to deal or, are you trying to deal with McDonald's?
You should be dealing with the general liability insurance carrier of the third-party contractor. It is not unusual for them to want to send their own adjuster to evaluate the damages. You should let them make their own estimate and if there is any discrepancy between your repair shop and their estimate, hopefully they can work out a compromise with the repair shop.
If the insurance carrier is unreasonable, you could file a complaint with the state insurance commissioner's office and they could hopefully follow-up on the problem. It would probably not be economically viable for you to attempt to retain an attorney on a small property damage claim, as the cost of the attorney may equal your damages.
You have a good claim against the restaurant and the contractor. The value of your claim is measured by the decrease in value of your automobile, and the loss of use of your auto while it was being repaired. The decrease in value of your automobile is usually determined by the cost of repair.
If the claim is a small one, some insurance companies will try to avoid paying full value, thinking that it will not be cost efficient for you to hire an attorney. If your claim is worth $5,500 or less, then you are entitled to recover your attorney fees under Oregon law. This greatly increases the likelihood of the insurance company paying your claim quickly. You will need an attorney to pursue this option.