What to check
When comparing prices, also check rarity, what you already own and the rest of the offer. These circumstances may differ, so the available examples do not show which factor caused the price difference.
PokéBonk — Are shop prices fixed?
The short answer
The screenshots show different offer states: one shop had prices of 39 and 26 with a refresh cost of 13, and another had four offers at 18 with a refresh cost of 10. These observations do not establish the pricing formula.