An experiment at NASA originally aimed at EM drive led to the observation that some laser beams slowed down while others did not, in a pattern identical to that predicted by an Alcubierre warp bubble as far as its interaction with light is concerned. The actual effect on light was observed in the microwave chamber. That microwave chamber works at much higher energy than an ordinary microwave oven, yet the entire experiment (including parts specific to EM drive and not necessary for Alcubierre drive costed no more than 50000 US dollars.
Even though the observed effect on laser beams is 40 times greater than explainable by any known effects of air, including that of air heated by the microwaves, the experimentalists Harold White and Richard Juday are planning a new experiment in vacuum. However, building a copy on the International Space Station (in a fashion similar to how Apollo 13 astronauts modified their CO2 scrubber to fit the landing capsule) and using the much better vacuum in space is a better idea.
The warp drive concept is also combinable with making the warp bubble big on the inside and small on the outside. Similar to van der Broeck's micro warp drive, though with a more efficient generation system than the classic negative energy formula based on gravity being the weakest force that van der Broeck (just like Alcubierre) remained using.