For the third time, we are told that there are two trips, one of which is "significantly more costly". It doesn't matter if the prices fluctuate, the fact that one is the "significantly more expensive" one, as opposed to any other description which does not utilize price, indicates that the relative difference in price is useful for distinguishing them, and indeed more useful than some alternative method of distinguishing them. You would not refer to something as the "significantly more expensive option" if you reasonably expect it to be cheaper than the "cheap option". It would be one thing if we were told that there was a last minute offer or a seasonal variation at play, but we were explicitly not. The question is what is the logical choice given this information, and that logical choice is to go on the more expensive trip. It doesn't matter if you'd make a different decision under different circumstances, it's fine for something to be logical under some circumstances but not under others.

The whole purpose of this discussion is that the point that the article is trying to convey, that autistic people are more likely to consider other circumstances and are thus more logical because they avoid the sunk cost bias is incorrect, because this is not an example of the sunk cost bias. The non-refundable cost you sunk into two things in the past is relevant to the decision of which one to keep because you can use it to predict future prices. What the article claims most people do is in fact the rational approach, and what the article claims autistic people do is generally irrational, thus working against the thesis of their article.