We built a 3500 sq foot block house, with hollowcore and geothermal for about €85 sq foot inc furnishing.
I got main trades in for raft, blocklaying, roofing, wiring, plumbing and plastering and tried to do as much myself as I could. Still have the gardens to do this summer, but have that budgeted in too.
Mind you, for another 10 or 20 thousand I could have saved alot of time and stress, getting other jobs done by trades. e.g. Tiling, drainage, doorframes, suspended ceilings, slabbing etc etc.
My advice, is fo self build, to sub out as much as possible. You will still save a fortune in comparism to Contractor.