A major cost to consider is handling...labor in handling will add up over time...it will be considered in the model.
The only time a passenger should be assisted...would be for a defective unit where spares would be on hand to replace.
As for power...there is no problem...if the seats have the capability...installers have been mentioned.
Other avenues such as..Advertisement...should also help to offset the direct cost of the units.
Is it not the idea to try and create a self generating revenue stream?
doni
