I would suggest washing your yeast if the cost is a factor. Its easy, look for the videos on YouTube, they explain it in very simple terms.
Theoretically you can wash your yeast over and over without having to buy more.
That said I made a 1 gallon batch with a gram of knotty but I used a starter to make sure it took hold. The reason I used one gram was it was what was left in the pack after I made my bigger batch. Didn't get all of it out when I dumped it. Oops.
I thinking think the packs say it is enough for 6 gallons when it will surely make more. Cya/marketing type thing to get you to buy more. Truth is with a good starter and nutrient and washing you can really stretch that 11g pack.