In general, how often are air locks opened on a rocket? How much energy is needed to open and close the entry point?
The only energy needed to open or close an airlock door is that needed to overcome the mechanical friction in the hinges / overcome the inertia of the hatch. This is because the differential pressure across the hatch is vented to "close to zero" before the hatch can be moved. If this wasn't done, the force holding the hatch closed would amount to many tons, making it impossible to move.
You can see in the Shuttle EVA checklist here (DEPRESS procedure) how the airlock depress valve is opened, and the hatch is not opened until the differential pressure is less than 0.5 psi.