Free: Contests & Raffles.
Unless you find a pro photographer selling his gear I wouldn't expect most used cameras to have more than 25k actuations, in a sense only 1/4 of the estimated life expectancy. You can find 40D's on CL for $400, and if less than 25k actuations I think that's a very nice camera to start out with at that price, 20D's are even less.The difference between the xxD series and the "Rebel" cameras is the size and materials used. The xxD's are more weather resistant too and balance better when used with a "white lens"