Currently building a mini ITX PC in a case I bought from gumtree.com ages ago, the Mobo CPU and ram cost just £24.99 on eBay!
The case was £15 from gumtree and the PSU £14.99 from eBay too!
The setup is 1.6Ghz Atom, 1gb DDR2 ram, dual GB Ethernet, onboard gfx with DVI and VGA out and sound ( http://www.ieiworld.com/redirect.ashx?code=3&id=0C075000297564249986&dest=null ) 250w PSU, the mobo and CPU use only 12w power, perfect firewall box I thought, I am going to pinch drives from an old PC I have.
The mobo shipped with a PicoPSU 90w Internal PSU without the charger unit which costs £19.99 normally, this clever thing is a totally silent PSU, and it sells for almost as much as I got the mobo/gpu/ram bundle for on eBay! PicoPSU 90w Internal PSU circuit board sells for £18.99 on eBay alone!