A Cars.com running costs study offers up a factoid about the Fiesta 1.0t:
The $2,475 price premium over the base 1.6L Fiesta is not recovered in 8 years of driving @ $3.30/gal and 15k mi./yr
Top 10 Cheapest New Cars You Can Buy - KickingTires
In the same study they also point out that even the $1k premium for the CVT in the Mirage doesn't pay for itself over the officially thirstier 5-speed manual in 8 years.