1. If you're eligible to upgrade, you can do that.
2. If there are other lines on your account, and one of them is eligible to upgrade, you can use their upgrade.
3. You can buy a used phone from Verizon, starting at around $50.
4. You can use an old phone that you, or someone else on your account has previously used.
5. You can use an old phone from a friend, or buy one online. Keep in mind that with this option, the phone will not have any kind of warranty and is ineligible for insurance. Also, with any phone purchased online, there's a risk of it being lost or stolen. So get the ESN from the seller before you buy, and confirm it with Verizon, if that's what you end up doing.
The Intensity costs $100 as a certified pre-owned device- thats what #3 above means. You can also only get 1 certified pre-owned device per year, so i would highly recommend getting insurance this time