This is a post showing up how the XP stone price can be higher on the Bigby's Handy Box.
This is not a post about the XP potion non-stacking issue.
This is not a post about how changing the level range ends up giving less XP.
Using the boxes to get the non-pet items they have in stock, you can define how expensive the Stone of Experience is on itself. And the Bigby's stone is more expensive. (The reason to not consider the pets is because the most expensive individual pet in Store is only 495 TP, and is cheaper than any of the other options)
Otto's Goodies: (4,995 TP)
5 Superior Experience Elixirs (1,995 TP)
5 Major Slayer Count Boosts (480 TP)
5 Huge Jewels of Fortune (225 TP)
5 Siberys Spirit Cakes (795 TP)
3 Greater Siberys Spirit Cakes (750 TP)
65 Astral Shards (395 TP)
1 Stone of Experience = (355 TP)
Bigby's Goodies: (3,995 TP)
5 Sovereign I Experience Elixirs (2395 TP)
3 Siberys Spirit Cakes (495 TP)
-100 Gold Seal Elixirs of Superior Healing (795 TP)
-25 Superior SP Potions (595 TP)
1 Stone of Experience (310 TP or 510 TP, depending on your choice)
My suggestion would be to add something else with the SP potions to cover the 200 TP gap. Maybe 30 Astral Shards?