Any way i can make this Gaming rig cheaper?

[ibox55]

I am building a gaming PC and have a budget of about £500/$800.
I would like to know where i can save money with this build here.
Also, I would like to know if there are any issues/anything i am missing as this is my first build.
Also, Can i use the OS from my old PC i use my old HDD?

 

[RazerZ]

Yes you can re use your hdd but not OS.
You picked out a bulldozer series CPU which are terrible. Go with this

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD FX-8320 3.5GHz 8-Core Processor (£109.19 @ Aria PC)
Motherboard: Asus M5A78L-M/USB3 Micro ATX AM3+ Motherboard (£50.90 @ Amazon UK)
Video Card: XFX Radeon HD 7870 2GB Video Card (£149.98 @ CCL Computers)
Case: Fractal Design Core 1000 MicroATX Mini Tower Case (£27.77 @ Novatech)
Power Supply: Antec High Current Gamer 520W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (£55.82 @ Scan.co.uk)
Optical Drive: Lite-On iHDS118-04 DVD/CD Drive (£11.10 @ Scan.co.uk)
Other: Windows 7 (£50.00)
Total: £454.76
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-10-01 22:34 BST+0100)

Also your missing ram. I don't know if you already have it, but if you don't add 8gb ram ( 4gbx2 sticks)