I don't understand why these wallets cost so much, they're normal wallets with a "gimmick" that doesn't cost anything.

I don't think they're so much "wallets with gimmick" but more "gimmicks that are wallets". I believe these wallets are custom made not just a wallet with an "attachment".

Some of these wallets are built from the ground up. Some are not. Standard, non gaffed leather wallet, can cost $40.00. At least here in korea. If you do want to go on the cheap just find a good wallet that you like and do it Mullica style. Also there are several SOH methods for card to wallet. I know that Chris Beason doesn't get gimmicked wallets and still does card to wallet. Personally I like the whole "Nest of Boxes" plot which means that I wan't a zipper or a snapped compartment in the wallet. Those are surprizingly hard to come by. The few coin purse/wallet designs I come by these days are all pink! I'm not "Metro" enough for that. Anyways, there are plenty of, "on the cheap" ways to do CTW, And if you shop around a bit you may even find some of the marketed CTWs are comparable in price to many non-gaffed wallets. Good luck!

And people are willing to pay nice amounts for these gaffs to be built in. There is a market (customer demand) at the current prices so then the product gets made and the product gets sold. If one wanted to they could add a gaff to their own wallet and attach a zipper so it appears as if it is necessary to unzip the compartment before remove the contents. It would look amazing and no one would be the wiser.