Trading Evans to get value is probably a few years too late. He had the worst season of his career a year ago and missed the last three games of the season on injured reserve. He had only 37 receptions and turned 30 years old this offseason.
As Buffalo Rumblings notes, the Bills probably could only get a late-round draft pick in exchange for Evans after his down year in 2010, but that's better than nothing. With Stevie Johnson, David Nelson, Roscoe Parrish, Buster Davis, and a few reasonably-promising younger options, the Bills don't have much of a role for Evans, and they might have to cut him outright if they don't find a trading partner.
For more on the Cardinals, check out Revenge Of The Birds.