Hey man,
Could you send me a link to the existing site, or an archive of the project so I know what we are working with here?
Your timeline won't be a problem, I could build an entire site for something of that nature in your time frame. Anyway, I'm available to chat or for a quick call if you would like to discuss details. I only have one other project on at the moment so let me know as soon as possible since you have a strict deadline on this one.
edit: Oh man, the additional details just showed up for me, and my lord that is horrendous. I'll start over for sure or you are right you are gonna lose that client... Whatever you decide to do best of luck man.
Thanks,
Erik