Hello,
The account associated with all these projects is on the Cloud Free plan which has a limit of 15 project hours per month, as stated on our website:
https://rstudio.cloud/plans/free
I checked your account usage for the current usage cycle (09/18 - 10/18) and you have exceeded this limit. You can see your current period usage by going to the Account Overview page:
https://rstudio.cloud/accounts/291159/overview
We are working on making improvements that would benefit users who get locked out due to usage, allowing them to download their projects in a more convenient way. If you need to download your projects, please open a support ticket using the Technical Support link in the left navigation menu and we will provide assistance.

Regarding upgrading to a paid plan, we provide several discounts to qualifying organizations and individuals, so please check out our pricing page and the various discounts we offer:
https://rstudio.cloud/plans/premium
Best,
Omar