Indoor costs more, not outdoor. Indoor you have to pay for lights and electricity, outdoor you get that free. Even when you're flowering and the light cycle is the shortest, it is still like $50+ per month per 1K watts, even more during veg, so if you're growing anything large scale that adds up fast. Then add in fans and filters, which is an upfront cost + electricity + replacement when the filter wears out. Then add in environmental control, AC or heating, dehumidifying, etc. Then add in space, since no matter how you cut it indoor space is more expensive per square foot than outdoor space. As a matter of fact, this may, in the long run, be where the biggest savings are to be had. A small house or warehouse is much more expensive than several undeveloped acres. All in all it adds up to indoor having a significantly higher operating cost than outdoor.