It depends... Are you taxed for both? If you aren't then I would favor the argument that it is one full price and one for free, but if you are then I could see the point of those that say it is two for half price.
Well, a lot of people seem think they should be getting things for "free". I don't think they actually realize that most stuff isn't free, it's usually paid for (by raising taxes on everyone).
Oh, and I think it's two for half price, because the free one is conditional on the purchase of the non-free one.