City Car Math Query

The Scion iQ, the way I want it, costs (before tax & all that stuff) $19,175. It gets 38mpg.

Aston Martin, whose cars I've been in love with since I was little, but who, until now, have never made I car I could or would actually drive, do a re-badged version of the iQ called the Cygnet. It's $48,000. From what I understand, Aston sprinkled magic fairy dust on the engine, and it gets 57(!!!1!)mpg.

I'm on a mission to buy the Scion sometime next year. I'm already go to sleep thinking about it. But if I somehow can, if my great American novel hits the spot & sells a million, I'm gonna get that Cygnet. And I will hug and squeeze it and call it George.

I will not call it George.

The Aston swag ("...the 'Emotional Control Unit' starter system", for example), badge & grill is alone worth all that extra money, but I'm thinking that once you've owned the car for X number of years, that $18,000 will be recuped in gas savings.

How many years+months is X? Assuming say $4 per gallon & driving your standard 1000 miles per month? I won't drive that much, but just for the sake of the math problem & in the spirit of typicalness.

Typicality?

Anyway, how do I set up that math problem and/or what is the answer? Just curious.