There's nothing wrong with on-site storage, but IMO you need a decent reason to start storing things locally as a new business.
Lack of upload speed, 38Mbps in this case, and the fact they're a media agency (likely to be dealing in large files) would be a good reason
not to opt for cloud storage.
And cost-per-user isn't the problem; as you said previously, to make the best use of cloud storage you need upload speeds and if you're having to factor in a synchronous connection, then costs spiral for a
small business.
And if upload saturation is an issue,
@BIGWEB mentions they're using Gsuite so they could easily push (client specific data) to GDrive and keep day-to-day working data local - best of both worlds.
As always, best solution for the budget and only Bigweb knows that so....
@BIGWEB, I'd strongly recommend against "beige" boxing a solution as some are suggesting; go for off-the-shelf with a warranty and support like a Nas device.
And always remember the rule-of-three for backups; simply replicating to your home isn't enough and you really want to be periodically backing up to another storage device (external drive etc) or cloud (BackBlaze, Amazon Glacier, GDrive/OneDrive etc).