Case isn't very important. You can go with a cheaper one.
The cheapest possible power supply that could work (and not be a danger to your computer) is the Antec VP-350w
http://www.scan.co.uk/products/350w-antec-basiq-vp-350p-gb-90-eff-120mm-fan-atx-v23-psu
That should be enough power for either the gtx 560 graphics card or a Radeon 7770 when paired with an Intel CPU. It would not be enough to overclock the 560. You would have enough extra power to overclock the 7770 if you wanted to though, as the 7770 uses less power. That Antec has only one PCI-e connector.
If you did overclock the 7770, it should perform nearly as well as the 560, so don't stress too much if the 560 is permanently out of stock. You should be able to find one for about 90 pounds after tax.
The cheapest possible power supply that could work (and not be a danger to your computer) is the Antec VP-350w
http://www.scan.co.uk/products/350w-antec-basiq-vp-350p-gb-90-eff-120mm-fan-atx-v23-psu
That should be enough power for either the gtx 560 graphics card or a Radeon 7770 when paired with an Intel CPU. It would not be enough to overclock the 560. You would have enough extra power to overclock the 7770 if you wanted to though, as the 7770 uses less power. That Antec has only one PCI-e connector.
If you did overclock the 7770, it should perform nearly as well as the 560, so don't stress too much if the 560 is permanently out of stock. You should be able to find one for about 90 pounds after tax.





