Well that is pretty much "outdoor" growing soto speak in that you are growing using the sun. But there is no requirement to use an HPS to grow a photoperiod plant, you can grow one with a $15 cfl just fine. The only difference between autoflowering and photoperiod that i'm aware of is that autoflowering strains have genes from ruderilis which allows them to flower under any light cycle, other than that they are still both cannabis plants. Photoperiod plants flower based on the light cycle, and not the amount of light. If money was an issue you could simply buy a plastic trashcan and hang a light from the lid and cut a hole in the side and glue a pc fan into it. (kinda like Ricky's idea in trailer park boys
)
Cannabis can be grown incredibly cheaply if you wish it so, but the more plants you have, or the bigger plants you have, naturally the more you'll then have to start spending be it on equiptment or electricity.