This is the list of components that I ordered. The only thing you might need to add is the storage device. As I already have an iSCSI capable NAS, the QNAP TS-659 Pro+, this is all I need:
3x OEM Networkcable CAT5e Blue 0.5 mtr (artnr. 337736)
3x OEM Networkcable CAT5e Yellow 0.5 mtr (artnr. 337730)
3x OEM Networkcable CAT5e Green 0.5 mtr (artnr. 337727)
3x Intel PRO/1000 PT Dual Port Server Adapter (artnr. 37894)
3x Case Antec ISK 300-150 (artnr. 257466)
3x Intel Core i3-2100T Processor (artnr. 392591)
3x Kingston ValueRAM KVR1333D3N9K2/8G (artnr. 230178)
3x Intel Desktop Board DQ67EP Executive Series (artnr. 396345)
3x NETGEAR ProSafe Plus GS105E 5-port Gigabit Ethernet Switch (artnr. 243035)
This hardware will set you back around €1500,- which fits nicely in my low-cost budget for the project.