Help choosing a lens for Canon 5DIi

Have done a search but have not found the answer.

I have a new 5D and mainly shoot dance performances in dim light (of course I can't use flash). Have been looking at the Canon 70-200 2.8 but it is a bit pricey.
Do any of the third party lens come close to this lens?
Are there any other Canon alternatives?

Thanks for hour help in advance?