I don't know what exactly Tom Rose is working on. There are various ways to measure CO2, like light absorbance oof gas molecules. That one doesn't work because of the hummidity. The CO2 sensor has been implemented and tested. It's just not offered yet publicly.
As far as pricing is concerned, that would probably depend on the volume to a large extend. Most manufacturers turn out rebreathers in fairly low numbers. The company that has developed the CO2 monitor wants to offer it as a complete electronics package (setpoint, deco & CO2). As such it would compete against the Hammerhead (setpoint & deco - $3,000) and Vision upgrade for the Inspiration (setpoint, deco and scrubber gauge - $4,500), which aren't exactly cheap either.
If they can offer it for around $4,000 it should be competitive.
But first the product must be cleared for sport diving use, and CE certifications may be required.
Also, all current electronically controlled CCR manufatcurers either already have upgraded electronics available, standard or on the drawing board.
Evo - standard: setpoint, deco and scrubber gauge
Inspiration - optional: setpoint, deco and scrubber gauge
PRISM - optional deco planned
Meg - optional: Shearwater setpoint & deco
Optima - standard: HH setpoint & deco
Ouroboros - standard: propratory setpoint & deco
So getting a manufacturer to offer the electronics isn't gonna be easy.