Event Zoom Lens

Hi all! I have Sony A-77, Sony DT 16-50/2.8 and Sony HVL-F58AM. I love my gear but I would love to have a good lens with more zoom for wedding or event photography. I have been suggested the Sony 70-200/2.8 G. Can you people please tell me your opinion? Any alternatives? (And cheaper ones too!). I search for a nice lens that will have a fast and accurate autofocus and to be f2.8. Thanks in advance for your help!