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]
(..) People used to giggle when you'd hear about black holes. They're like unicorns, mythical creatures. We called this the "giggle factor." People would say, "beam me up, Scotty." Well, no one is laughing anymore. Krauss: (..)2010 TvShow: How the Universe Works Title: Black Holes Season: 1 Episode 2