Have a look at the guides in serverbuild.net forums such as forums.serverbuilds.net/t/guide-nas-killer-5-0/

The series of post that is Nas killer (4.0 5.0 6.0) etc. they list a bunch of CPUs and motherboards with approx eBay prices along with ram disks etc etc. I used it as a reference when building my cheap Nas for home, mainly the motherboard/CPU sections.