Fuel efficiency and pricing are two sides of the same coin. Few car makers do both. As
Michael Clark has said in these Youtube videos, the Mirage is not only an affordable/less expensive car ( it's not the least expensive, but 2nd or 3rd cheapest new car to purchase based on MSRP), but it is also less costly to maintain. Therefore fuel efficiency is one of the few things that pays off over time, whereas a low-purchase price is a one-time deal. So getting a low-buy in price and a higher fuel economy is going to save you much more in the long run. That said, some of the MSRPs are going to be less desirable for the higher trims, so you will get a better value if you are just looking for the the best bang (in mpg) for the buck. This video explains it quite well - with one addition- the AC is now standard (the 2014 did not have it).
The way I see it is, every time I get 47mpg at a tank fillup, I am getting 17mpg more than my last car. When you buy a more expensive car, it depreciates more in absolute amounts (not percentage- i.e. a Tesla might not depreciate as much as quickly, but you still end up spending a lot more.
Edit: Also, I paid less than the MSRP, so it is very possible to buy the car or a 2019 model (new) for less than the cost of a new Spark or Versa.