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]
(..) that we're working with? Thank God, I got you. Tonight, the first photograph of the aliens goes viral. "Biological contamination is a major risk factor at the Montana site". So, say environmental pressure groups. to protest the government's handling of the crisis. First contact with whoever it is (..)2016 Arrival