Are you looking for a real cameo (carved from shell or stone) or a resin (plastic) one? Are you interested in classical (traditional) designs, or are modern cameos o.k.? For example, the Pandora one listed in another post, is a more modern face/motif.
I'm not sure if cameos are hot now (I'm inclined to think they aren't--I used to collect the "real" ones), so you may get lucky, and find them in antique stores cheaper than in recent years. However, be prepared to pay $$$ for an unusual, very well-made antique one. For example, if the face is of a historical figure, such as Robert E. Lee (once saw one of those for $800+), the cost will be much higher than the standard "woman in profile" ones.
Also, look for detail, such as the carving of the nose on profile. I've noticed that's where the artists tend to rush a bit in the carving. Also, that nose can tell you the age of the cameo: more modern, from late 19thC. on, have more perky, upturned noses. Earlier, such as the 1860's tend to have classical Greek or Roman figures, and what is called a "Roman nose". They also don't tend to be "dressed up" (cameo habille, in French)--that is, with an attached necklace on the woman, sometimes with a tiny diamond in its "pendant".
if one of you does see one with athena but for less im definitely interested.