J.W.
Here is the problem you are going to run into. If you went there without insurance there is a lower amount you would pay. By going there with insurance it applies to your deductible so their hands are tied. They cannot apply 600 to your deductible and then only charge you say 300, it is against the law, it violates the contract they have with your insurance provider.
Now take a deep breath, have you received your EOB? There tends to be a contractual write down also required by that same contract. That may not have been applied yet.
Sorry if this isn't what you wanted to hear but the doctor's office won't be able to help you, the best you can hope for is that bill was generated before it was submitted to your insurance.
Just read your what happened, did anyone say six hundred is not a lot of money because it is. It is just not possible to lower it if you claimed this under your insurance. :(