I need to get a better lens for my Rebel. I'd really like to get the Canon EF 24-70mm f/2.8L USM Standard Zoom Lens, but the $1600 price tag is a bit out of the range of what I can afford. Anyone one have any suggestions as to comparable, but cheaper lens? Mainly, I will be using it for portraits, mainly still images that will be included in a documentary I am making. Thanks for any help.