I have seen some people build Ceph clusters using the HC2 board [1] before. I'm not sure what the performance is like, but it seems like a neat way to scale out storage. The only real shortcoming is that there's a single NIC... If there were two, you could use an HA stack for your network and have a very robust system for very cheap.
[1] https://www.hardkernel.com/shop/odroid-hc2-home-cloud-two/