Netduino 2 $59.95
Unless you can dumb it down to a point where people can use it without reading a 1000+ page datasheet, there is no chance of it competing with arduino.
The arduino is going after one particular metric: ease of use. You don't need a 100MIPS mcu to blink an led once every second, or to turn on a relay when the user has pushed a button, etc.
Raw performance is not important (or it is not paramount) here.