Do not underestimate the ancillary construction costs. You now have a slope
Our wall structure slope = gravel, insulation, waterproof concrete, furring strips to create an installation level, drywall panels
Surcharge compared to a normal wall somewhere around 15-20 k
Structural engineer wanted thicker floor slab, thicker base slab, lots of reinforcement + 25 k
Prices 2017/2018 11m house length ground class 5/6
For you, there is still slope stabilization and excavation disposal (a buddy paid 20 k in 2018) plus possibly additional costs with the projections and recesses
Outdoor area retaining wall + earthworks are not comparable price-wise to level plots.
Whether you want to hear it or not, give yourself some room in the budget and generously at that.