It's 20 dollars more than a standard controller. It allows you to play with two players, has motion controls, HD rumble, and an IR camera.
They do more, and particularly if you're into multiplayer gaming, they're a better value. If you want to play something like Mario Kart with four players, you'd need to spend 80 dollars in controllers. If you want to play a similar four player game on the PS4, you'd have to spend 180 dollars in controllers.
If you want to play Just Dance with four players on PS4, you need an Eye camera, and four Moves. If you buy all that at MSRP, you're looking at 250 dollars. For the Switch, you can play Just Dance with four players for 80 dollars.
Someone will inevitably say "what if I don't want to play local multiplayer, or don't want motion controls". If you're one of those people, then you probably shouldn't buy the joycons, and should reconsider whether or not you should buy a Switch.
That's the consistent problem. People who prefer PS4 or XBox One gaming are judging the Switch based on their desires. That's fine to determine whether or not they should buy it. But if you want to make a general statement about whether or not the price is fair, you have to look at its functionality. For people who care about local multiplayer, portability, and motion control gaming, the Switch and Joycon prices are pretty reasonable.