The ESX II pictured above was getting some good mileage (~70 MPG), and the ESX III that Dodge built 5 years later (in 2003) was getting 72 MPG. The cost premium on the ESX II was around $15,000 more than the normal Intrepid, and less on the III. I'm not sure why they didn't build it, but they were using diesel motors so maybe they were having trouble with emissions.
Dodge ESX3 Concept wallpaper # 01 of 03, MY 2000