If your PIP coverage is not enough to cover all of your medical expenses, there are a few options available to you. If you have health insurance, you can use this as another source to pay for medical expenses.
If you don't have health insurance or don't want to pay out of pocket, you can pay the balance out of your recovery if your medical provider is willing to wait until you receive that recovery. Many medical providers will agree to this if you are represented by an attorney who signs a letter of protection. This letter indicates that you and your attorney agree to pay the medical provider out of any recovery you receive.
Not all medical providers will agree to wait for payment, and some may send you to collections or even sue you for the money. However, many providers will agree to wait, especially if you have an attorney representing you.