McDonald's announced that it would be giving away 10,000 bottles of its Big Mac Sauce at participating stores nation wide. So a very limited number for people to own. I thought I would search Ebay for Big Mac Sauce to see what the going price is for one of these bottles. Some of the bottles are going for over $100. Seems pretty steep, but if you really love it and want the official product, then maybe that's not much to spend.
But, a quick Google or YouTube search and you can find a recipe to make the sauce at home. Below is a video produced by McDonald's Canada, that shows how to make the sauce.