Boeing claims that the 787 burns around 20% less fuel than any other same sized aircraft. Thing is, airbus for example doesn't offer any aircraft in that size bracket (210-250 seats for the -8). It can be roughly compared to a 767-300, but no completely, especially if range comes into the equation. The 787 is a pretty small wide body airplane with a pretty long range in the non-overweight configuration.
The first around 60 aircraft are overweight, the first 20 of those by a huge amount. One of the results is the low number of seats that are used by the first two customers on international long haul routes, 158 in the ANA version and 186 in the JAL one.
Total cost will depend of course, the first 300 airplanes were sold at steep discounts for prices as low as 64 million $ per airplane which is considerably below the list price for a 737.