They manufactured their own hot dog manufacturing plant:

> "What we figured out we could do is build our own hot dog-manufacturing plant (in Los Angeles) and make our own Kirkland Signature hot dogs. Now we are doing so much hot dog business that we’ve opened up another plant in Chicago. By having the discipline to say, ‘You are not going to be able to raise your price. You have to figure it out,’ we took it over and started manufacturing our hot dogs. We keep it at $1.50 and make enough money to get a fair return."

https://www.425business.com/news/costco-ceo-craig-jelinek-on...