Google offers free 15GB storage with each account, here I'll mention some official and unofficial ways to get more storage -
1. You can buy 100GB additional storage for only $1.99/month and 1TB for only $9.99/month. To buy visit https://www.google.com/settings/storage once you are logged in to your google account.
2. You can buy G Suite Business from google's G Suite which includes not only the storage but also many additional things from google, so we recommend this for everyone. The cheapest plan is $5/month on which you will get 30GB storage only but with the second plan you can have 1TB storage for only $10/month. To buy G Suite Business, visit this page - https://gsuite.google.com/pricing.html
There are a few websites who offers multiple Google Apps account for a one-time affordable price, but as they are official there is no guarantee or warranty about their services. Still, they are cheap so I think you should try them out -
1. The first website I'm gonna mention offers very affordable plans and perfect for more storage. On their first plan, they offer you 50 Google Apps account with 30GB storage in each account for only $45.00 USD one-time payment. Check out their plans and prices here - https://gappiness.com/order/ . Contact them before buying to be safe.
2. This one is a bit pricey than the first one, but their service is good. They offer 10 Google Apps account for $39.99 one-time payment and 50 Google Apps account for $54.99 one-time payment. Check out their plans and pricing here - https://gapps.xyz/ . Contact them before buying to be safe.
maybe there are other ways to get more storage on google drive, you can always search in google for those.