If you want lenses for a Ray Ban that cant be seen in, you have no choice but to have them mirrored.
The second thing is it depends on what type of model you are after, only about half the range come with polarised lenses, and about half of those only come mirrored.
Polarised lenses arent mirrored in anyway. From a distance they may effectively be good enough to not be able to see through, but all polarised lenses do is stop certain glare coming into your eyes from certain surfaces at certain angles (the glare when sun hits water for example, or the sun coming off the snow). So polarised may be good enough depending on what you want to use them for.
If you let me know what you plan on using them for, and what sort of model you want...Im assuming aviators? Then I can probably let you know what sort of tint the polarised lenses have on them, and could tell you if they are going to be good enough for what you want them for.