The Mazda 2 now for sale in the US is already one of the two most affordable green cars on the ACEEE list, but Green Car Congress talks about an advanced evolution of the Mazda Demio with, "hybrid-like fuel consumption at a lower price." 

Mazda began taking pre-orders for the facelifted Mazda Demio (known overseas as the Mazda2) at all Mazda ... dealers throughout Japan; the sales launch is scheduled for 30 June. The updated Demio offers a new 13-SKYACTIV model grade that features the new 1.3-liter gasoline direct injection SKYACTIV engine.

Combined with an updated version of Mazda’s idling stop [start-stop] system, i-stop, and a continuously variable transmission (CVT), SKYACTIV-G 1.3 will achieve fuel economy of 71 mpg US on Japan’s 10-15 mode test cycle, or 59 mpg US, on the newer JC08 test cycle. By comparison, the Prius S model is rated at 84 mpg US, on the 10-15, and 72 mpg US, on the JC-08. Starting price (including taxes) for the SKYACTIV-G 1.3 is US$17,430; starting price for the Prius S is US$27,400. Mazda is hoping that the Demio’s lower price point will give it some traction in the market against hybrids.

Commenter Roger Pham notes that "Mazda has used almost every engine tricks known to wring out kinetic from every drop of gasoline while maintaining the same cost as non-hybrid entry-level gasoline cars." Commenter Treehugger notes that "the Mazda2 2011 1.5L sold in US is given for 29/35 MPG." As previously mentioned, the US MPG numbers scarcely take starts and stops into account.

I drove next to a Mazda 2 on the highway today, and while pleasing to my eye, it looks even smaller than the Toyota Yaris. Reviewers say it is very comfortable inside, though, so it would be tempting for a compact person to get hybrid Prius-like fuel efficiency while spending $10,000 less. But will Mazda bring this configuration to the US market? And with Mazda having broken with Ford, where will they build it? And will it really be that much less than Prius?

Kelley Blue Book interviews a Mazda suit:

In a similar vein, Bertel Schmitt at The Truth About Cars uses his subscription to The Nikkei to reveal that Suzuki is thinking of introducing a plug-in hybrid version of their tiny Swift - but not at a particularly low price:

Suzuki will finally relent and will offer a plug-in hybrid version of its bestselling Swift hatchback ... expected to cost $6,200 [JDM] more than the regular Swift, with the total price not exceeding  $24,900 ...