CPU: i5 2500K. £161.21 LN37506
Mobo: GA-Z68P-DS3 - £75.22 LN41414
RAM: 4gb 1600mhz DDR3 - £24.48 LN37493
HDD: 1 x 500GB - £31.43 LN28751
PSU: EZcool 500W - £25.67 LN8039
GPU: XFX HD 6870 £137.62 LN37721
CASE: Coolermaster Elite 430 £38.38 LN34936
CD/DVD: SATA DVDRW £13.99 LN39605
OS: Windows 7 32 BIT OEM £73.28 LN29160
Which comes to about £615.00 with postage.
The LN numbers you can just put in the search bar at Scan Computing.
This is just to give you some idea.It is more than possible to shave a few quid off but not enough for a monitor.