If you refuse coverage, you will be required to expressly reject it in writing. Typically this means signing a form with your insurance company that they are required to keep on file by the state.
If you decide you want to keep PIP, the state requires you to carry at least $10,000 of PIP coverage. This would cover you per accident.
While you are trying to save money, it can be beneficial to carry even the state minimum PIP. If you are injured in an accident, your personal injury protection would cover your medical expenses, regardless of fault.