Nearpod's Silver Edition is free!
The Nearpod Gold Edition is for teachers and costs $120/year, billed yearly. The Gold Edition gets you a lot more storage space, 3GB instead of 50MB. It gives you access to Premium features. They allow you to include web content, YouTube videos, Twitter feeds and Virtual Reality Field Trips in your lessons. You can share a lesson with your students in Student-paced mode so they navigate it at their own pace. And as a Gold Member, you can create larger lessons and for a class of up to 50 students instead of just 30 students.You can upgrade here.
The School and District Editions are purchased by institutions for groups of teachers. You can look into them here.