How did you do the air sealing yourself? were you concerned about your continuous air/vapor/water barriers?
I taped all the exterior sheathing joints (including at the foundation with high-performance air-sealing tapes). Then I applied a fully adhered vapor permeable airtight membrane to the entire exterior sheathing surface, and caulked the wall/roof joint, which also provided redundancy for the joint taping.
The general contractor applied a secondary bulk water shedding house wrap, a rain screen, and the finish cladding.
There were other things I did internally during the drywall/plasterboard stage also to minimize air movement through walls and ceilings.
I'm just finishing doing a high performance renovation ( <1 ACH50, all electric, heat pumps, HRV, etc.). For new construction, the difference is more like +5-10% - the materials are marginally more expensive, and the labor doesn't require extremely specialized skills. The HVAC equipment is the very expensive part.
For a renovation, it's more like 20% more expensive but it can vary widely depending on the existing house's condition and the original build quality.
I personally saved a boatload by doing the high performance air sealing work myself - it's not that hard once you get the hang of it, just laborious.