I picked up a x850 256MB for 300 Euro from ebay over here in europe they usually go for around 380 euro new so do some currency conversions (US prices are cheaper) . As for cooling I have seen shuttle's barebones (sb95pv2) being sold with the x800 and x850 ATi series. Though as mentioned earlier you got to watch the size of the vid card. Also I would be worried bout overheating as (usually) Intel and ATi do run hotter than AMD and NVidia.
Tell me how you get on cause I got a SD31P arriving soon and am getting a wee bit worried reading this thread