It occurred to me today... I've been trying to reduce the cost of the controller board by shrinking the board. And that works, but the most expensive component is the LCD display backpack.
That got me thinking... Is there room on the backpack form factor for both the backpack's display i2c adapter circuitry and the Toast-R-Reflow controller?
And, sure enough, there is.
The board price goes up a bit - it's now $7.50 each instead of closer to $3 - and you need to add a LCD display ($11 on DigiKey for a monochrome backlit model - the Toast-R-Reflow doesn't really need the fancy RGB backlighting) and a handful of other SMD parts.
The net result is that it looks like I will be able to put complete controller assemblies for $40 each as opposed to $25, and then you need to buy a $30 LCD display backpack (or the $25 AdaFruit shield).
If you feel brave, the board is shared at OSH Park, but the basic controller design hasn't been fully tested yet, so no guarantees, at least at the moment. But if the basic controller design works, then this variant will be my next attempt.