I can't speak on the cost of the actualy IFE, but I remeber asking about the weight penalty an airline has to pay for a B6 style IFE system.

If I recall correctly, it was in the neighborhood of 7 pounds per screen. This includes that little box under the seats, and all the wiring.

So a jetBlue plane with 156 seats would be carrying around an extra 1092 pounds of weight.

I'm sure someone here can figure out how much that weight costs in terms of fuel burn.