http://en.m.wikipedia.org/wiki/Inflation
I'd recommend taking an economics class if you don't understand that the price of goods generally increases over time. $25 in 2001 money is $33 now. So these new controllers are actually cheaper when adjusted for inflation.
Also, I have no clue what you're talking about when you say controller prices have come down. Most first party controllers are $60 now (which is absurd)! Sure you can buy knock off Yobo shit, but that's like buying Mad Catz back in the day. Third party controllers are generally trash, you really do get what you pay for when it comes to controllers.
I still regret buying Astro Pads for my Dreamcast. I saved $5, but woof - those were terrible quality controllers.
Hardy har har.
But assuming you are serious and not trying to rile me up further, let's take your link and move on up to Economics 201 here: Inflation isn't exactly a set number, at least beyond the most basic sense. Costs fluctuate constantly based on gazillions of factors, such as the industry you are in. In the tech industry, it hardly exists (more or less - this is debatable based on how you look at costs and components) as prices typically go down for a variety of reasons. The tech in controllers is part of this. Putting aside the endless debates on layout preferences, by today's standards, the gamecube controller isn't anything special. But having rumble built in as opposed to the way N64 did it, on top of those pressure sensitive shoulder buttons, was a pretty big deal at the time even if it is pretty much standard today.
Now, the cost for a good deal of these components has went down over time. Hence the PC controllers I mentioned. You can buy a controller functionally identical to the Gamecube (sans rumble I suppose, I honestly don't recall since I don't use it) with a few extra buttons and bells/whistles from several companies for under $20 on PC. Being a CAG, I have scored several Logitechs for under $10 myself. Meanwhile the PS3 controller that MSRPs for $50 or so (often on sale for $35) has EVERYTHING the Gamecube controller does + wireless functionality, a built in battery, and sixaxis motion. Needless to say all of this adds a good deal to the cost, though I think most of us here would agree that the Dualshock 3 is still grossly overpriced. And frankly your "argument" about 3rd party controllers sucking is just... well... ignorant. I will be the first to curse Madcatz name, but there are plenty of other good options out there that nobody considers because they blindly scream that all 3rd party options suck.
Now using your logic, a PS3 should potentially cost more than a PS4 right now becuase INFLATION! That's just bullshit. It really is the same principal here. Arguments about layout and nostalgia aside, Nintendo is releasing a (again, by today's standards) pretty barebones controller here and charging a pretty nice premium for it. Not a huge deal if you only need one controller, but for anybody who wanted 4 (or even myself who wanted 3) this sucks pretty hard. $30 may be cheaper than all the overpriced console controllers in the market, and I'm sure that's how Nintendo calculated their pricing, but it still sucks.
Now lets factor in that this is Nintendo we are dealing with here. This is the same company that released Wii Speak... the e-reader... the DS rumblepack.... the Circle Pad Pro..... the SNES mouse..... I can go on and on but hopefully you see the point. Nintendo utulizes these perephrials on one or two games then forget they even exist. Hell, even Wii Motion + was ignored outside of Skyward Sword and a couple of casual titles with "Wii" in the title. But at least in most of these instances 3rd parties picked up some slack and made use of them, I don't even see that happening with this adapter (especially not in any scenario where it would be preferable to the wireless WiiU Pro controller). For anybody who wants to argue that GC is "so obviously" coming to VC, I urge you to take a hard, objective look at Nintendo's history with emulation, even if it's just the current WiiU/3DS eshop. Not to mention that they just raked in a ton of dough with a relatively basic $50 HDified port. Then come back and seriously say that Nintendo is going to not only port over Gamecube to the VC but will take the time to create a save system for it to replace the memory cards like what Sony has done on PS3. It could happen, but it isn't bloody likely, it sure as hell won't come cheap, and either way maybes shouldn't factor into your purchase unless you are prepared to be burned.
It's just frustrating to me because, as somebody who has ventured outside the console market, I know these prices are way up there. I know, it was stupid of me to ever think Nintendo would price these fairly when they are known for charging top dollar for everything. I was just hoping that, after seeing tons of new (unopened) GC controllers going under $10 on ebay for forever now (still plenty there right now BTW, so stock up now

) that Nintendo might possibly charge a reasonable price ($20) for these. Being the huge SSB fan that I am, I would have been satisfied even if they just charged the same $25 they always had. But obviously I was wrong, so now I am going from buying an adaptor + 3 controllers to nothing.