Rather than looking at the $25-$50 binders, for a game like this you should probably just be looking at sheets that will go into a regular binder.

I got mine from CoolStuffInc, but apparently you can find them for pretty cheap on Amazon (surprise). I bought Ultimate Guard pages in Black, though it seems if you don't care about color others might be cheaper.

There are other brands, but basically, you're looking at a up to ~$10 for 10 pages and a binder (go D-Ring) that is also inexpensive. As far as binders, 1.5" seems like the right size at the moment but I wouldn't be surprised if by the end of Carcosa a 2" makes more sense.

For what it's worth, with three core sets and one of each expansion/mythos to date, I am able to fit most classes onto 2 pages each, being willing to put 4 cards into one sleeve. It's one fully utilized page front-and-back for level 0 cards, level 1 cards take up one page but don't fill it in, and I skip to a new page with each class. Seeker currently takes up 3 pages because their level 0 cards take up just over the 18 slots one page offers, Dr. Milan has his own page in my binder at the moment. Haha

There's also a page that fits investigator cards, if that tickles your fancy. And I bought regular page sleeves for the rules booklets and campaign guides. I need to print the Dunwich Campaign PDF up to add to the collection, now that they released that.

Whether it's worth it or not? Seeing Amazon's low prices I feel like I might have overpaid, but it's a satisfying reminder of the time I played CCGs having a binder of cards that I can build my deck from. I can definitely see looking at it as a luxury compared to cardboard boxes like others are saying.