I can offer tested working HP DC7800 SFF computers:
240x HP DC7800 SFF – C2D E6850/2048/160/DVD
Price – 68 EUR each.
Price with MAR Windows 7 Home preinstalled – 81 EUR each.
Price with MAR Windows 7 PRO preinstalled – 92 EUR each.
For take all make an offer.
Let me know if have any questions.