Paying for interviews do suck. I don't remember losing all that much money to this whole process all those years ago. WashU took the prize; they paid for everything and sent you the plane ticket in the mail. I don't think they'll do that for pathology interviews though. I estimate some pretty heavy hits to my wallet this year anyway.
I think it's a good idea to opt for the 2 day interview. An extra day in CA can't hurt now right? If Stanford invited me for an interview that's what I would do. Unfortunately, the two friends I had in the Bay area left so I would definitely have to front the extra hotel costs.