No, sorry, I don't think they are worth that much, used. As a general rule pre-owned pearls don't hold their value unless they are a famous brand like Mikimoto or unless someone famous or historically important owned them.
Also, freshwater pearls are the most common pearls there are-- eBay is flooded with them.
What we usually recommend is to do a search on eBay for SOLD pieces like the ones you have-- and see what they actually sold for. That will give you your best estimate of what they are likely to bring if you sell them.
A used item is only "worth" what someone will pay for it.
Pearls don't have intrinsic value like precious metals.