£494 after 10% Quidco
Dell Vostro 460 Desktop
Dell E2211H 21.5" WLED 1080P monitor
Core i5-2500 3.3GHz Quad Core
4GB DDR3 1,333
Radeon HD 5450 1GB
Windows 7 Pro
350W power supply
~£539 or ~£494 after 10% Quidco (Exc VAT and delivery)
To get this price you need to go via Quidco (Dell Small Business), search for E-code D044603, downgrade the warranty to standard collect and return and use the £60 off voucher PVF3KQMCFK341R
If you say the monitor is worth £100 it means you are getting a decent desktop for around £400. The downside is that it is 32bit Windows only although the license is for either so you can install yourself if you have a disk.
The system minus graphics will only consume about 100W with the CPU on full load; I have an i5-2500K and I checked.
So that gives a reasonable amount of headroom to add a gaming graphics card in the £100 to £150 range using the 350W P/S that comes with this. Be careful if adding an older discounted graphics card as the power consumption can be a lot higher.