B+W is the gold-standard... but expensive. Also the physical diameter of the filter will have a big impact on the price tag. A B+W high end CPL will be over $100. Part of the price tag of a B+W has to do with the durability of the filter... coatings to keep dirt off, avoid reflections, resist weather, etc.) So you're paying for more than *just* the optical performance alone.
BUT... the Hoya Pro1 series are actually EXTREMELY good (optically probably just as good as the B+W filters). They will cost substantially less.
I *think* the 18-55mm lens has a 58mm filter diameter (someone please chime in and correct me if I'm wrong).
As I check Amazon... the price on the B+W 58mm CPL is about $115. The price on the Hoya Pro1 58mm CPL is about $58 (roughly half the price.)
You can search for YouTube videos that demonstrate the difference between good filters and bad filters.
Also... be aware that polarization has everything to do with the angle of the light (which is why you have to rotate the filter to "tune" it). It turns out if you use a CPL on a very wide focal length, you get banding (a dark area where its really has a strong effect) and very weak areas where it doesn't do much at all. Polarizers are really good for normal through telephoto focal lengths... and also work for mild wide angles... but watch out for extremely wide angles as you may not like the results.
Good luck!
