Can't really argue on the relative cost of stainless steels versus non-stainless steels.
Can't really argue on the difficulty to machine, except to say, stainless in industry has been around for a long time now, and things have been learned that make the job faster and easier. Learned, as in the right tooling material and cutter shapes.
To the above, many parts are IC or MIM process, so machining is minimal or non existent.
I can say, one major "cost" of production is not the cost of materials, or specialty tooling, but rather the speed of production. These days, its all about how fast something can be produced. How many units per hour, or per day or week, etc.
And, I can say, that the price of any item in the market place has absolutely nothing, zero, zip nada to do with "cost of production", but rather what the market will bear in terms of price. In other words, if by some magic it a company could produce a stainless steel firearm for less raw cost than a blued one, it would still charge more for the stainless one - because the market would pay the price asked.
One interesting item we see is that the "expensive to produce" polygonal barrel was used in the superior model version of a certain brain of guns. As it turns out, the traditional land/groove barrel is produced by the same process (hammer forging), and actually costs more because it is produced at a slower rate. Go figure. And, that's marketing for ya.