Well their largest, basic milkshake is $8.50 plus tax. At Toothsome, for $3 more - you get same size essentially (Ghirardeli is tall and narrow, Toothsome is shorter but wider), take home glass, and a few extra ingredients. They aren't that much different in price.
For example, my Banana shake had a chocolate dipped banana, which at theme parks run $3.99-4.99 on its own, and one blended in as well.