Synclavier tests the boundaries of credulity today with the release of a $400 MIDI Knob for their $30 app.
It seems like a fine and sturdy knob. You could potentially whack this knob pretty hard without fear of it falling off. Its exaggerated girth ensures you'll always be able to get a solid meaty grip.
If you're an American, where "knob" has a slang connotation, you may expect that the $400 knob of which I speak must be a wildly expensive dildo. While I assure you that it is not, it is worth pointing out how much this thing will fuck you.
For the sake of comparison Korg makes a controller that costs $52, and features 8 knobs. You even get a some sliders and buttons, but on a purely knob-based economic consideration you're getting knobs at $6.50 each from Korg. Similarly the Novation Launch Control XL packs in 24 knobs at a comparable $6.66 per knob.