The locket you have there is called a "Mourning Locket". The photo of the women and the style of the metal work would date it to around 1870 or 80. These are very popular items and are widely collected. You didn't mention if there was makers mark anywhere, if you can find one and do a bit of research on the internet it would definitely increase it's value. I'd take it to a reputable jeweller and have it appraised.
I would guess that the value, without knowing more about it, would be $50 - $75. If it's marked and the cameo is real and the gold is real (not plated), then the skys-the-limit on the price.
Good luck,
Dave