I am curious about your results, as I am purchasing a roll from Fuji this week for this very purpose.
I think this method will be the cats ass for making alt negs, I have put Rollie ortho on my machine and made black white negatives, right now am waiting to pay for my large processor to explore further this option.
What I like about the Chromira or Lambda option on RA4 fujiclear is the ability to place different colour on different areas of the film to accent contrast or density, this opens up a whole area of control.
Since I have not the apples to apples proof *YET* that it will work therefore I defer to your experience, but with the strength of some of the plate burners available I do not think exposure time will be a problem with the right set up.
As far as cost , in the long run if it works as I expect then any lab in the world with RA 4 options could offer the service which would certainly bring the price down.
For me the cost is very small , basically the price of the roll , what I would sell at probably once profiles and expectations of methodology are met would be also reasonable, considering these negs would probably for photographers best work and not just for testing.
I've tried it on my Chromira and there are 2 problems.... one is that it is very expensive material. The second thing is that those materials have a built in UV protection layer that adds about 3.5 stops of UV blocking and it will make your exposures very long....... I called Fuji tech directly and they are unable to make the film without the UV layer even asa custom product.