Excavate land costs vs Downward slope hillside

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Question for seasoned developers. My partner and I develop in the Los Angeles area and we are currently building our first project on hillside downward slope. With that said we looked at another lot today but it is building uphill. It would require to excavate the land and build a retaining wall. I know I am completely over simplifying this question and it should come with lots of details. But for the sake of the time I am keeping this incredibly simple. Which method is TYPICALLY less expensive - Downward slope development or excavate for uphill development? Any input is appreciated. Thank you!