Since the class does not specifically state otherwise, yet still made learns it as a 4th level power, Energy Burst costs 7 PP.
This is slightly confusing. The text says 1 ML per 3 levels, which would mean an ML of 0 from level 1-2, ML 1 at level 3, ML 2 at level 6, ML 3 at level 9, ML 4 at level 12, ML 5 at level 15, and ML 6 at level 18. However, the example states otherwise. Judging from the example and the levels at which new powers are gained, was the ML supposed to be 1 + 1/3 class levels?
Edit:
New maneuver levels come every 2 IL. A 2/3 IL progression gives a new level of maneuvers every 3 levels (1st level maneuvers come at level 2, up until 7th level maneuvers at level 20). A 3/4 IL progression gives 3 levels of maneuvers over the course of every 8 levels (1st level maneuvers come at level 2, 2nd at 4, 3rd at 7, 4th at 10, 5th at 12, 6th at 15, 7th at 18, and 8th at level 20).