What is the cheapest (reliable) PSU can i get to run a HD 4830 living in the UK?

THe corsair 450watt is the best and very enough for your needs its price is about 60$ here some description about the psu VX450W - The Corsair VX450W features a temperature controlled 120mm fan for near silent operation, up to 87% energy efficiency, and a powerful single +12V rail. This makes it the perfect PSU for home theater PCs, mid-range single graphics card gaming solutions.