Comment by Retr0spectrum

If you don't mind buying slightly old and power hungry stuff, server grade hardware is actually much cheaper.

24GB DDR2 ECC RAM - £16 (I was VERY lucky to get this one) 2x Xeon X5450 - £22 Intel S5000PALR Motherboard - £30

These specs are roughly equivalent to a 2008 mac pro, which costs around £500.