You do not buy stuff. Instead, you simply use gems to get Rare Items. Gems can be obtained by playing the following:
- Bubble Bug
- Magic Pop
- Candy Swap
- Bullseye (you have play to one of the higher levels)
To get rare items, go inside Orion's Rare Finds, and click on Orion. Put any 3 gems inside the orb and get your Rare item!