If you're looking at cheap, then the Canon 75-300mm is the way to go.
A good lens to start off with. Sells for under $400.
Next step up is maybe would be the Sigma 50-500mm for just under $1k or even cheaper if you shop around.
Then you have the Sigma 80-400mm OS (Optical Stabilized) for a bit more.
But a lot of people recommend the Canon 100-400 IS L series lens, for around $2k. L series lenses are the best quality Canon glass. And it's all about the lens people say. My advice, save up, dont get the plastic 75-300mm Canon, and get one of the Sigma's or the 100-400
