If you want specifically a 5600, get the BFG Asylum 5600 ultra (flip chip with faster 400/800 clock) @ CompUSA for $129.99. BGF's design is very quiet and has some OC ability. (Nice ramsinks on memory as well). There are faster versions that are clocked by other manufacturer's by OCing them out off the line a bit, however this is the best bang for your buck in terms of price/performance when it comes to specifically a 5600 ultra.
My advice is trying to get the Radeon 9600SE @ Best Buy for $129.99 out the door with a FREE copy of Half Life 2 ONLY, AND ONLY if you can get the earlier cards that are Radeon 9600 pros that were packed inside of them. Radeon 9600pro is slightly faster than the 5600 ultra across the board in terms of performance, and quite a bit faster with HL2 benchmarks. Good luck.