U.S. News gives a rundown of affordable cars here: http://usnews.rankingsandreviews.com/cars-trucks/rankings/Affordable-Small-Cars/
For Kelly Blue Book's best economy cars in several categories, see: http://www.kbb.com/car-reviews-and-news/top-10/most-affordable-cars-2014/2000010311/
AutoTrader gives a list of the ten best for a first time buyer: http://www.autotrader.com/research/article/best-cars/215404/10-best-new-cars-for-first-time-buyers-2014-edition.jsp
Edmunds provides a list of top ten consumer favorites: http://www.edmunds.com/car-reviews/consumers-favorites/best-economy-cars-2013.html
Consumer Reports provides the top ten list of used economy cars (and if you are a first time buyer or on a tight budget, this may be your best bet): http://www.consumerreports.org/cro/2012/04/best-in-used-car-fuel-economy/index.htm
Best of luck to you in your search.
And, if you should get a Toyota Yaris, see the Toyota Yaris Maintenance Mysteries label for advice.