Peridots are generally not too rare nor expensive. Stones less than 1 carat can be had very affordably (under $50). High quality stones between 1 and 3 carats acan be found in high end jewelry costing several hundreds of dollars. Size does not play a critical role in the valuation of peridot other than this except when the size is significantly larger. A peridot over 6 carats will be extremely rare and could be worthy of a museum, and easily everal thousands of dollars.