Cheap:Newegg.com - ASUS EAH5450 SILENT/DI/512MD3(LP) Radeon HD 5450 512MB 64-bit DDR3 PCI Express 2.1 x16 HDCP Ready Low Profile Ready Video Card
Newegg.com - SAPPHIRE 100293L Radeon HD 5570 1GB 128-bit DDR3 PCI Express 2.1 x16 HDCP Ready Low Profile Ready Video Card
They both are very nice i would get the latter for cheap but good and check out other parts of newegg for other cheap-pricey ones.