Adam - there is no such thing as an 'efficient' gas turbine. They are used in aircraft due to very high power to weight ratios - exactly the opposite to electrical power!!!!
The specific fuel consuption of gas turbines is terrible, the numbers give you a clue gas turbine around 0.8 lbs/hp hr, a petrol engine 0.4 and diesel 0.32 - the basic thermodynamic cycles that these engines use predetermine these 'efficiencies' and wishful thinking will never outdo physics.
People who actually understand these things are the main reason why some of these outlandish ideas have not seen the light of day.
LArgely I~ would agree that the 'Pious' is largely a confidence trick. If Toyota had genuinely wanted to advance the state of the art it would have been diesel powered. But it was aimed squarely at the US market - where cars are petrol powered and so the marketing people waved its partially green credentials and the somewhat gullible public bought them - giving them fuel consumption almost as good a a standard diesel car........
Why do turbines cost so much? Try the engineering and materials. There will never be a 'cheap' turbine. Removing them from the aeronautical industry would help but in essensce most of a turbine needs to be made from very high specification materials and the slightest design or operational error reduces them to scrap - a massive difference to cast iron and standard aluminium alloys.