Surely the cost to Apple of A-series vs M-series isn't that significant though? I'd think they'd need to cut a lot (or their margin) to get down to that price point on a laptop.
One big difference is volume. They sell way, way more A-series devices than M-series devices and so they may benefit from economy of scale.
With all of Apple's service offerings these days, they could also potentially justify slim margins by positioning the A-series MacBook as both a loss leader and gateway drug.