http://inductiveautomation.com/forum/viewtopic.php?f=70&t=7031&p=20732&hilit=heartbeat#p20732
The references in there should also give you some ideas.
On the other hand, I just put together some Nettop PC’s for about $250. That’s about mid-range in the thin-client prices, if I remember correctly. Along with a 19" touchscreen monitor that put me at about $1200