Thin Client cases and Mini ITX boards

[Oko]

I would like to build two systems specifically as high quality "anti-virus gateways" for my home network and my office network using OpenBSD of course. Even though, I run only OpenBSD as desktop OS I want to relax
little bit firewall rules on Desktops. I would like to be able to print, scan, and do
other stuff on the local network. Thus, I really want robust firewall/router/squid/snort solution.

I found a couple really nice and inexpensive (under $50) Intel MiniITX motherboards with pre-installed Atom processor but I am stump with the price of MiniITX cases so I have a different idea.

I saw really nice inexpensive Thin Clients on Ebay. I was wondering if anybody has any experience in using them for MiniITX build. In particular there are couple HP thin clients that are under
$30, look beautiful, and big enough to swallow even a HDD. I will be probably using USB though.

I am open for any kind of creative ideas.

P.S. The other option is just to get two dirt cheap old Netra SUN servers for about $50 from Ebay and go from there.