If you just look at the clues the way they are written, you are right. But you have to look at your grid and consider what you already know... which is that Riesling equals Frances. That means you can rewrite the clues like this:
#1 Frances paid 1 dollar more than the diner who ordered the sea bass.
#8 Yolanda paid 1 dollar more than the one who had the port.
Now you can see that port and sea bass are both 1 dollar less than two different items in the same category.
Hope that helps!