What will an insurance company offer to settle for a possible neck injury?

I was rear-ended by another car. I reported to the insurance company of the person who hit me that my neck was a little sore. They offered me $700 to sign a release form without me even asking. I told the claims adjuster I needed to think about it. Short of getting a lawyer, what could I expect to be offered? I am sure insurance companys have a set amount that they will pay to get me to sign the release form. Anyone know about how much that would be?