These are the simplified pricing and storage numbers for Mendeley subscription plans as of 2019-01-10:
This information is available only from their upgrade page and can only be viewed when logged in. I'm posting it here for others who may be interested but don't want to create an account (or log in) just to view it. See the included screenshots for Mendeley's presentation.
* The initial "unlimited" storage in the Max plan starts with 100GB and requires you to email them for more.