a non linear Droplet Pricing compared to storage and transfer

Introduction: From a marketing and competitive standpoint i surely understand that one of the lower tiers of droplets look very great value/product . But from a programming standpoint the non linear scaling of droplets storage between prices are forcing me to change the setup of my application .

To give an example of what i mean :

5$/month : 512mb , 1 Core , 20 GB , 1 TB transfer

20$/month : 2GB , 2 Core , 40 GB , 3 TB transfer

Now maximum storage is a necessary requirement for my application . So spinning up 4 droplets of 5$/ month would give me .

4 x 5$ droplet = 2GB , 4 cores , 80 GB , 4TB
That is over double the amount of storage for the same price . Could someone shed some light why this is done this way because Hosting the app on 1 server or 4 servers requires a different networking setup .

That brings me to my final question does digital ocean offer plans/upgrades for more storage ?