Ease Me In (The more guarded approach):
No matter what you decide about birth control, I just want you to be informed. Maybe you can call the health center. They're experienced, understanding, and very easy to talk to about the risk of pregnancy and STIs. They can give you information and tips on how to be safe without compromising your beliefs. Some of them also can help with the cost.
Just Give It to Me (The no-nonsense tactic):
If you're having sex and not using birth control, you're essentially saying you're trying to have a baby. After all, 85 of 100 couples that are having sex and not using birth control get pregnant within a year. Plus, not using any protection puts you at risk for STIs. Are you really ready for that?