That is a fairly typical low class strain of zhen-zhu or "pearl fo the orient" if I am not mistaking. I wouldn't give any more than about $50.00 for it.
Here's a pic of my pearl before he got sick.
Tanks he got a terrible case of HITH and I had to euthanize him. A word of caution make sure you have PLENTY of filtration on any tank you put yours in if you get it.