Try checking some of the research done by the CSIRO back in the 80's. The concluded that one large bomber would be cost-effective, but that was based on saves on a relatively small number of fires out of the total possible.
This seems a more expensive package.
Bear in mind the drop parameters.
Supposed minimum height is 400'AGL, and the USFS Large Air Tanker project found that they shouldn't be used on country with an overall slope of more than (IIRC) 7 degrees.