Precious stones glitter in shops on the streets of Mykonos and Santorini, and you can choose as many carats as your budget can handle.
You can't buy any stones in Santorini, they aren't for sale. 
mnli hypothesis: You can't buy any stones in Santorini, they aren't for sale.  premise: Precious stones glitter in shops on the streets of Mykonos and Santorini, and you can choose as many carats as your budget can handle.