It can seem unusual that the smallest canvas stretcher bars sometimes cost more than slightly larger sizes within the same range.
This is because very short stretcher bars are harder to manufacture. They are made up almost entirely of corner joints, which are the most intricate part of the construction process. With smaller sizes, those corners sit very close together, making production slower and more complex.
Because of this, some smaller sizes are priced higher than nearby larger sizes. This is a normal part of stretcher bar manufacturing rather than a website or pricing error.