i buy my toyota filters for less than 4 dollars each. I just look for dealer coupons that I get from 3 local dealers every couple of months (we have an mr2 and highlander). Dealers also advertise in the local "Advertiser" paper in SF.
There's also a dealer in NY, if I remember correctly, that gives a good discount when you buy 6 filters. I know they used to advertise in the back of some auto magazines, but I can't think of their name right now.