Just as a small guideline. I really did everything myself (except the kitchen and interior doors) including the complete plans (you only need an architect, structural engineer, and site manager to sign off on the building permit). Material was of course purchased and many things were also made by myself. It might not really be comparable but the calculations (turnkey) from prefab house manufacturers and general contractors were roughly around 480k€. In the end, doing everything myself, the final price came to just under 600k€. You see, the more you do yourself, the better materials and more unusual things you choose because you are building the house for yourself. (For your information: After completion, the bank sent an appraiser who valued the property at >1m€)