What plan are you on? They were advertising 18 GB for $100 but I don't see that available anymore. Additionally, that was if you were on the new Verizon Plan. If you are on a legacy More Everything plan, you would have to change to the new Verizon plan which may change some of your other charges/fees than you are currently paying.
Edit: sorry, I do still see the 18 GB for $100, but again, that is only on the Verizon Plan NOT legacy plans.