If apple made a cheap laptop, it would be aimed at schools. This would make it compete with Chromebooks and iPads.
It'll be hard to compete with Chromebook prices. The software subsidised by Google's services and the hardware vendors are happy to ship flimsy cheep hardware. If apple shipped similar quality it would hurt their brand.
Apple wouldn't be able to compete in price or software services. They would be reliant on MS Office or Googles web apps.
They would be selling the better build quality and better battery life.
This laptop would be a safari machine. The only differentiator from an iPad would be the keyboard and windowing system.
I don't see apple sacrificing brand or iPad sales. The best solution is improving the iPads productivity capabilities to close the gap.