That looks like a delightful little item , worksoutathome .
At first glance , I'd say you've made a good choice by not unloading it for the price you'd been offered .
If you could take it to another jeweler , who specializes in pearls , you might ask for a 'general value' , as for insurance or replacement value ... lacking that I'd say pay a jeweler to have it inspected , appraised &/or certified .