At $15 per bulb, which is about double the normal bulb cost, but these lamps last forever, which makes the cost per use next to nothing
The original 13139 lamp is of the EFP type and lasts 1,000 hours.
The EFN type lamp is not the original, but serves as replacement... and lasts just 50 hours (read the specs).
So, the cost is far from next to nothing.