Lincoln 4c stamp blk/wht. Lincoln in profile. Any ideas of estimate?

Answer 1

There are too many variables to give you an accurate estimate.

Unused or used?

Condition? How centered is the picture of Abe on the stamp? If it's unused, what is the condition of the glue on the stamp? Are the perferations on the stamp cut or torn? Are the perfs uniform? [good] or are they of different lengths [lowers value]

Year?

Your best bet is to go to the library and see if they have a Scott's catalog. It's the bible of stamp collecting.