So true, and it's also too expensive to buy cheap (lousy) filters in any size. I always try to purchase the best glass that I can. Which ones are you using?
WM
I normally only buy B+W. They have pretty decent material. I've seen CP filters on sale here for not even 20$. I think if you spit on your lens, you'll get about the same quality as those.
I paid 100$ something for their 77 10-stopper. I also have a CP of theirs but it's their cheaper one for the 77mm. They had that one in the store and I wanted to test it before investing money in a good one. Even when they advise thinner ones for wides, I must say I don't suffer any issue on my 18-35mm even when using the widest part. The only thing I need to pay attention to is how I turn it when I have large skies, else it can create a color difference. I decided to keep it instead of paying the price of a lens for the best CPs.
I have another B+W of them for my 50/35mm which I bought in the past and some of their close-ups and this far, none of their material disappointed me. I have some more of their stuff in the pipe-line including a metal lens hood for the Tamron. If that one works out well, I might replace all my plastic crap by either metal or rubber hoods.