That's about as low as I could get it:
PCPartPicker part list:
http://uk.pcpartpicker.com/p/1XjAD
Price breakdown by merchant: http://uk.pcpartpicker.com/p/1XjAD/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/1XjAD/benchmarks/
CPU: AMD FX-6300 3.5GHz 6-Core Processor (£83.99 @ Aria PC)
Motherboard: MSI 970A-G43 ATX AM3+ Motherboard (£50.36 @ Scan.co.uk)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1600 Memory (£59.99 @ Novatech)
Storage: Seagate Barracuda 500GB 3.5" 7200RPM Internal Hard Drive (£35.00 @ Amazon UK)
Video Card: Zotac GeForce GT 610 2GB Video Card (£41.33 @ Amazon UK)
Case: NZXT Source 210 Elite (Black) ATX Mid Tower Case (£38.65 @ Scan.co.uk)
Power Supply: Corsair CX 430W 80 PLUS Bronze Certified ATX12V Power Supply (£37.30 @ Amazon UK)
Optical Drive: LG GH24NS95 DVD/CD Writer (£12.74 @ Amazon UK)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) (£65.99 @ Aria PC)
Monitor: Hannspree HE225DPB 21.5" Monitor (£89.98 @ CCL Computers)
Total: £515.33
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-11-04 16:44 GMT+0000)