Doesn't look like anyone else has anything to add. You, sir, are indeed correct.
The bad thing is, this problem was posed in some fluff (philosophy, I think) course at a technical school I was at, and tried to explain that the logical framing of the question was faulty, but I never could get the teacher to figure that out. Of course, it only works if you frame it that way, or else people naturally order it in a more consistent manner, and there ceases to be any riddle at all.
When you point out the $27 paid, you are, in essence, pointing out where the money is NOT, rather than looking at where it IS.. The other $3 are with the gentlemen, as a rebate.