You can check out a Tamron 28-300mm zoom. Much cheaper. You get what you pay for and its a lot less expensive than a pro grade lens. Good luck at finding a competent review, the better reviewers don't have time to waste on bashing a lens.
I believe I shot this whole set with the Tamron 28-300 on my 5DIII if you want a sampling of what it does:
You can see what he means, it is definitely a few steps down from something like the Canon 70-300L.
It is, however, reallly compact, and for the price, a decently built and performing lens, and the IS is pretty decent. Has a lock switch so it doesn't droop on you. I used it happily for a few years before I got my 5D and some better lenses.