Cost was the 'decisive/deciding/determining factor' in their decision. [=the most important reason for their decision]
The 'deciding factor' was cost. [=the decision was based on cost; the least expensive option was chosen]
Costs increased/decreased by a 'factor' of 10. [=costs were 10 times higher/lower than they had been]
(..) Captain? We've all heard about the computer simulations and now we were watching for actual simulations but I can't quite believe. You simply haven't taken into account human factor. Human pilot simulations showed that you could have made it back to the airport. No, they don't. (..)2016 Sully