I have often seen it where when you enter your city and date, that it shows you the lowest price, but that doesn't mean that when you select it, that that is the the price you get.

So, if you select a non-smoking room instead of smoking, or if only a certain type of room is available, then that is what the pricing would be.

I'm not sure if this is what applies in your case, but it is what I have noticed before. I've never had it say that my rate is $50, and then be charged $80.