I’d suggest you look at 70-200 lenses with a constant aperture (so that the image doesn’t darken as you zoom in) – preferably something around the 2.8 Aperture. Budget is going to be the issue with Canon lenses but you can try looking for the slightly older version of their lens, or buy a good quality used lens from someplace like KEH.
Check out some reviews for the Sigma and Tamron equivalents just to see what they have, I think they will fit your budget much better with more than acceptable performance for video which is relatively low resolution anyhow when compared to still images….but that’s another rant so I’d better stop myself there. 🙂
Steve Crow
Crow Digital Media
http://www.CrowDigitalMedia.com