You can try enrolling your account to automatic payment to have the $30 plan ($5 discount because of auto-Reboost)
You can check this link out for reference. https://www.boostmobile.com/?ID16=spot6:All:auto reboost#!/support/faq/account-management/re-boost-a...
To do it by yourself
Login to My Account.
You can also change or cancel your Auto Re-Boost by dialing #ADD (#233) from your Boost® phone.
or you can call 1-866-402-7366 for General Support
or you can go to this page right here https://www.boostmobile.com/?ID16=spot1:All:customer care#!/framework_contact_us/
Hope this helps 😃
I agree with @Dartis if you add your credit card you will receive a $5 discount witch will make your payment $30 but boost mobile would have to withdraw this from your card in order to be valid thats honestly the only way.
Boost Mobile was offering a plan of $30 unlimited talk, text and data but with 1GB 4G it only lasted for a little while. That plan is no longer available unless for does that already have it. 🙂