The selection was limited for us from the very beginning because I did not expect to be able to afford the budget for a custom-designed solid house
In fact, the opposite is more the case: "He who pays the piper calls the tune" – the architect directly commissioned by you is also a better friend to your wallet than one employed by the house provider.
Almost every housing magazine annually shows cases where the most successful combination of living quality and cost-saving construction was achieved by an independent architect.
Individual planning with your own architect is not more expensive. What is (unnecessarily) expensive is only a mistaken individual planning: that is, when you have a cookie-cutter plan designed "exclusively."
"Free planning" must virtually always be the case if you do not have a universal-optimal plot. So, mostly.
And saving, as already says, comes from critically questioning frills like bay windows, corner windows & co. – you don’t have to completely forego them, just handle them with budget awareness.