Agree with JR.. $5 million probably wouldn't cover the change in infrastructure and operating costs to make this happen.
If you have ever been to butler, you realize that this isn't about retrofitting existing space, it would pretty much mean building another wing (not that there is even a logical place to do so.)
I'm no architect or contractor, but this seems high to me. I've only been there four times, but it seems like the entrance, dining area [including kitchen, which is usually a big number], and pro shop could basically all stay the same. They'd obviously need to enclose the men's locker room and add a women's locker room somewhere--perhaps by adding a wing--but I just don't see how that work gets you near $5 million.
Some of the comments also suggest that the place doesn't have a real kitchen or dining facilities. ("As it stands the club just offers premade sandwiches and a full bar.") That hasn't been my experience; in fact, every time I've been there, I've been told to "order whatever you want and they'll make it," and they have.
Ultimately, though, does anyone really think this is about actually attracting women members -- rather than simply eliminating a prohibition against having them, thereby allowing them both to host tour events and to get the influx of guys whose wives don't like male only clubs? For co-ed golf-only clubs where there's no pool, tennis court, or anything like that, and where each spouse has to join individually, what percentage of members are women? I bet it's low.