do you know if the pearls are cultured pearls or are they pearl imitations? Try to determine which type of pearls are in your necklace strand as this will be the most important factor when valuing.
I recently had a double strand of Majorica pearls valued for $150. Information on Majorica Pearls can be found Here... The clasp was 14 karat gold and decorated with tiny seed pearls. The pearls were in good condition and both the strands had recently been restrung.
In the photo below is a pearl necklace and earring set, discovered on ebay the pearls are white with beige undertone. They are imitations pearls and they had a buy it now price of $5.98.