Two plans.

Storage beyond what Pro includes is charged on the average you held across the calendar month, not on the most you held on any one day. Hold 150 GB all month and the extra is $2.50: 50 GB over, at 5 cents a GB. Hold it for a single day and it is that one day's share of it.

What is in the trash counts until it is gone for good, which is 30 days after it was put there, or sooner if you empty it.

Every download of your files counts, whoever makes it: you, somebody with a link, a visitor to a public page. Beyond 50 GB in a calendar month it is 10 cents a GB. On Free it stops at 5 GB and starts again on the first.

An app is a separate drive that your own program reaches with a key. Its files do not appear among yours, and what it holds and what is downloaded from it count toward the same allowances as everything else. 100,000 calls a month are included, and beyond that it is 50 cents for each further 100,000. Read the reference

The extras are held to a spending limit: $10 a month unless you change it, which is enough for another 200 GB of storage. At the limit, uploads stop, and so do downloads beyond what the plan includes. Nothing is deleted, and everything starts again on the first. Set it to nothing and Pro never costs more than its price.

You are told by email when a month reaches most of its limit, and when it reaches all of it.

Cancel at any time and Pro runs to the end of what you paid for. After that, an account that fits in Free's 5 GB simply carries on as Free.

One that holds more becomes read-only: everything can still be opened, downloaded and deleted, and nothing can be added. 30 days later we remove files to bring it down to 5 GB. What is in the trash goes first, then files, starting with the largest. You are told on the day Pro ends and again before anything is removed, and billing settings lists exactly which files it would be. Go back to Pro, or make room yourself, and nothing is removed.