Open source alternatives such as Ubuntu Server or even proprietary products like Synology have Samba available. With Samba you can still manage your Windows devices with RSAT like you would with Windows Server. The difference is that these platforms are much cheaper than Windows Server.
Consider reading this short blog post on an easy and cheap way to administer a network.
We have a basic network kit available that combines a pfSense style firewall/router, Samba, and Ubiquity Access Points. This setup is perfect for small offices and even churches with 1-20 computers.