Yes, there was an eBay auction where someone purported to have an original package of the Mulan Szechuan Dipping sauce from McDonalds.
Yes, someone used the eBay system to make a bid of $14,700.
However, there are good reasons to believe the original item was faked, and no good reason to believe the bid was actually paid.
The picture in the eBay listing matches this one from eater.com (and elsewhere on the Internet):
When compared to this photo of a BBQ sauce package from An Immovable Feast, it can be seen that - suspiciously - both list exactly the same ingredients,
High fructose corn syrup, water, tomato paste, grape vinegar, distilled vinegar, salt, soy sauce (water, wheat, soybeans, salt), food starch- modified, spices, dextrose, soybean oil, natural smoke flavor (plant source), xanthan gum, caramel color, garlic powder, cellulose gum, dried chili peppers, malic acid, natural flavors (fruit and vegetable source), onion powder, sodium benzoate (preservative), succinic acid
Furthermore, when it is compared with this picture of BBQ sauce package found at Mouthful of Sunshine, it can be seen that it shares the same reflections. The Mulan image on the right has been faked based on the package on the left.
The faked image also contains the copyright date of 2011, despite the sauce being discontinued in 1998.
It is clear that the picture of the item being sold has been faked.
Two other items make me suspicious that this was a deliberate ploy (or prank) by McDonalds and the creators of Rick and Morty:
The Rick and Morty show that contains the reference was aired on April 1.
A live-action Mulan movie comes out in 2018.