If it works by grabbing hold of some sort of cosmic fabric and thrusting against it then that takes much less energy but it flies in the face of the principle of relativity. Something that physicists are unwilling to part with.
On that topic for a moment, I read that Dr. Harold White managed to reduce the amount of antimatter needed to 500kg to generate a warp engine that would take a ship to Alpha Centauri in just shy of 5 months. However, are there any figures for this? What I mean is, does this imply only 500kg are needed if the engine is in constant use for the full five months, so, a use of 100kg per month?
The ships in my world do have a warp drive, however, they are still limited by the light speed barrier - i.e., a ship's maximum speed is the speed of light, but the warp engine negates time dilation effects. How would this factor into energy usage?