Hi Jesse,
It all depends 
Depending on the number of pages, the number of layouts, whether they need to write copy, perform usability testing, etc. And depends on the type of platform they are developing on OR if you are going to get a new platform.
The price changes with the number of iterations needed to layouts/design and the time frame you are looking at.
It also depends on whether you have a freelancer or agency do it. Without knowing the complete scope, I would guess somewhere between $50k-$250k if it is a pretty large site. If it is only like 50 pages and you only did a few templates, you could maybe get away with spending $10k-$30... depending on the people you work with.
First, I would look at design firms available in your area. Check out the websites they have developed and contact someone at the company they developed for and ask them about their experience. Do this for a handful of firms. Then contact each firm and ask them for a quote. After you have quotes from firms, go out and ask some freelancers... look at their work... ask for a quote. You will probably have to have some sit down, in person interviews with these people to make sure that they really get what you are asking for.
I know that doesn't completely answer your question, but hopefully it gives you a few things to think about.
Mike