Looking for recommendations / advice on Backup Storage

We have multiple servers (15+) that we are backing up to other servers currently. I want to move the destination to a dedicated offsite storage solution and am recommending recommendations.

Most are Windows Server 2012s but a few OSX Servers as well as a possiblility of replacing time machine backups on a few osx desktops

I am looking for recommendations of a solution to put in place here. We can only afford one server / solution at this time, but have a budget up to $20k with storage (I know not a lot). It will be racked off site (but one of our facilities connected via Fibre / separate from our Data Center)

Thanks for your advice