Most of the tech in the joycons will still be in there, so the savings from not having them separately will be pretty minor.
I'd see it at $199 only of the current model would go down to $249, too. A 100 dollar/Euro gap would be just too much between the two models.
By looking at the USB-C connector port at the bottom, that Switch mini won't be much smaller than the base model. I think it's even possible to use it with a dock from the base model, although the thumbsticks could be just too close to make it fit. But at least a real D-pad this time around
Edit: Am I the only one who gets reminded to the Wii U gamepad by it's design?
With the detachable joycons, each removable part needs to have it's own battery. And each joycon needs it's own set of HD Rumble motors, accelerometers and gyroscopes.
If if you stick them all together you can save a considerable cost. You only need one battery, one set of rumble motors, one set of accelerometers, one gyro. Plus, the "slides" that have to be manufactured to remove and apply the joycons onto the system, don't need to be made anymore. The screen is probably smaller too.
I think they'd save a considerable ammount of money to manufacture this..