The step they're talking about here, the AlON interlayer, is a trivial, almost zero increase in cost relative to the cost of the diode. It doesn't require a mask step, the materials (Al source, O2 and N2 gases) are cheap, and the deposition would be very short for such a thin layer. It's possible the deposition can be done in exactly the same tool they're using for the facet coatings anyway, so the added cost is almost entirely negligible. And the tool being used is a tool they already had for other depositions anyway, so there's no new tool to purchase.
Diodes in general are expensive, but the step they're talking about here is essentially nothing to the cost of the diode.