My experience with sloped plots of land: What you pay less in the favorable purchase price compared to other plots in the area, you often invest many times over later in earthworks. A soil survey can help identify costly conditions (groundwater, undercutting, rocks...) early on to avoid blowing the budget with the second groundbreaking. Since we built on a slope but did not proceed in a budget-oriented way, I can hardly advise you from my own experience.