How i can check if domain has been dropped before?Depends. If it is a dropped / expired domain, not worth very much.
If it's an existing domain with traffic but you've wiped out / lost the site, you could get a few hundred or more; depends on the niche
A good brandable PR6 with a running site, good traffic, and in a profitable niche could be worth thousands or even tens of thousands.
PM me the names if you want - I'll give you my best opinion...