I have great interest in Dixie cups as well. ESB and RotJ boxes, unopened and in nice shape used to regularly sell for around $20 - 30. Star Wars (A New Hope) sold for around $30. They used to be fairly plentiful on eBay, but now they are few and far between. And when they do come up people are asking outrageous prices, for some reason, even for the more common RotJ. Someone recently listed several RotJ for ~$70 each! Not sue if they actually sell at these higher prices.
I am kicking myself as I had a chance to buy nearly every one a couple years ago for around $20 each and they were in sharp, sharp condition! :-(
One of the rarer items are the regular Dixie cups, without Star Wars graphics on the cups, with the Star Wars story cards inside, sealed. I think a lot of kids wanted those story cards and not many remain sealed. Particularly hard to find in nice shape. There are several different ones, however none of the designs feature Star Wars too heavily on the front of the packaging. There are some of the ESB ones that come up less often than the others.