What do you need to know? There's no reason to pay for actual PassiveHaus status (an expensive plaque that won't increase the performance/value of your home), but we've 'achieved' the standard with a new build in Devon (~100 sqm 3 bed, so actually no mean feat given the space-to-walls ratio).
MVHR, vents, design, fitting and setup was ~£10k
Ultra high-spec windows/doors/skylights were ~£12k
PV array and SunAmp PV Unit (DHW) was ~£7k
PassiveSlab foundation was ~£1k (excludes £4k piles cost)
Timber frame (installed to 0.6 airtightness or better) for ~52k
Cost savings that helped to offset the above:
No thermal store
Bare minimum for plumbing
Almost no heating (3 small electric towel rails)
Very fresh air (always)
Much lower bills (~10% of the average)
Much better for the environment
Cooler in summer
Warmer in winter
I met with a few RetroFit companies when looking for a PH timber frame supplier, the retrofit stuff seems more complicated, but it's certainly possible.
Being able to plan/design/manage the freshness/humidity/temperature of your home is amazing. So many great (glazed) architectural builds feel somewhat stuffy by comparison!