Chances are that they are mostly common stamps that have minimum value even in pristine condition.
If you go to the main library they usually have a Scott catalogue which lists all the worlds stamps by country with a value. This is the price they will sell at to the public, dealers will give you maximum of 10% of this, usually much less.
Send me a scan or a couple of photos and I will give you an idea or you can look here.
https://www.poppe-stamps.com/?t=:1 Edited by vegimite, 2019-04-09 21:14:47