The base engine on the Aura is a V6, either the LZ4 or LY7 depending on model year. The hybrid engine is the 2.4 liter BAS from General Motors. The engines are paired with either a 4 speed automatic on the hybrid or a 6 speed automatic on the regular gasoline model.
The only body type for the Aura so far is a 4 door sedan. That body is built around the GM Epsilon platform, which is shared with the Chevrolet Malibu, Pontiac G6 and Saab 9-3, among several others.
The base model Aura is the XE. The engine on this model makes 224 horsepower, which is very good for a base model from Saturn, probably their best ever. The top model Aura is the XR. The DOHC V6 with VVT engine in that model makes 252 horsepower. Who knew that Saturn was capable of making such a powerful car?
The hybrid Aura is called the Aura Green Line, and it's referred to as a mild hybrid, meaning it does not rely as heavily on the electric motor as much as some other hybrids, so fuel economy is not as different from the regular gas models as it would be if it used the electric motor more. Fuel economy on the Green Line is 28 city, 35 highway.
The Aura is a little too new to be showing up in too many used car lots just yet. You can buy them in almost new and barely used condition, usually direct from dealers, especially those dealers who are dealing on eBay. That's usually the first place I look for used cars, even the fairly new ones.