Insufficient budget. Unless you want a tiny house. You’ve got to spend $2 for every conventional $1. 50K as you passive tax is way too little. You’re paying up front for the next 30 years, instead of monthly for 30 years.

If your goal is minimal monthly bills for utilities, you can readily achieve that without going to the extremes of a Passive House. A reasonably well designed house with efficient heating/cooling systems coupled with solar power system can do that. As an example, around here, a $50k budget could buy solar plus a geothermal HVAC system.

Greenbuildingadvisors.com is a very good source of information.

Passive solar design has been around for a long time. There's lots of good information available.

Here's a great GBA article that's very relevant to your goal:

https://www.greenbuildingadvisor.com/article/building-a-passive-house-for-163-per-square-foot

The total cost was just a smidge above $300k.

I think passive house is fantastic, if I build again for myself, I'd consider it again.

Ultimately I chose the PGH "Pretty Good House" approach for now. I liked this approach because I can sell anyone on it over conventional construction because paybacks and benefits are immediate.

The key features being intelligent design and 100% electric, results are noticeably better comfort and air quality.

The last 5% simply isn't cost effective AT ALL. PGH and using all the accessible and relatively inexpensive tools in your energy saving toolkit is the right approach if budget is a concern at all.

and you can buy a whole hell of a lot of HVAC equipment for that last 5%....

It is is NO WAY CHEAPER. NO WAY.

Higher upfront cost is offset by not installing a heating system, no Air Conditioner needed which results in long term savings.

If a house has no HVAC system, then how do you set the desired indoor temperature?

Just try living in any house in GA with no AC. 🤣🙄 The mold from the 100% humidity would kill you. Even when it’s 70 outside, it’s miserably muggy. Indoor air quality requires conditioning for multiple reasons. Not just raw temperature.

It's all personal choice. I'd be happy with a well built house that reasonably adheres to today's building science recommendations and techniques but beyond that I wouldn't go.

Often people build houses thinking they'll be there forever and later changes in life trigger a move. You should be careful to avoid building a structure with uncommon features that could be viewed as extreme or undesirable by potential buyers.

Apart from the mildest of climate regions, you will need a full ventilation system: heating, air conditioning, and an HRV or ERV for continuous ventilation. Passive Houses are almost never truly 'passive'. In fact, in addition to the above, you're likely to also need a dedicated dehumidifier because the loads for cooling are so low that your heat pump won't run hard enough to adequately address latent loads.

https://kimchiandkraut.net/2019/02/21/hvac-for-passive-house/

In our Passive House our HVAC costs ended up at roughly $20,000, so not too far off what it would've been for a conventional new construction build. We have a ductless mini split Mitsubishi heat pump combined with a Zehnder ERV and a couple of stand alone dehumidifiers (I'd go with a dedicated ducted whole house unit if I could do it over).

https://kimchiandkraut.net/2019/03/06/ductless-mini-split-for-passive-house/

Be cautious about cost to build per square foot claims unless you know all construction costs are accounted for (including site work and local fees --- these can add up quickly and surprise you if you're unprepared). In addition, there are wide swings in costs related to labor and materials depending on your specific location.

The notion that you can build a PH for only 5-10% extra is highly dubious. For instance, compared to what? A subdivision of new tract housing? A high-end everything custom home? The truth is it depends. For instance, how much square footage are you willing to give up in order to offset the additional costs of substantially more insulation, along with added time and materials for proper air sealing? You could also compromise on some interior finishes to offset the insulation/air sealing costs.

In addition, are you prepared to do a large proportion of the work yourself? If you're using a builder, have they previously completed a PH, or will they be learning on your house?

There's a lot to think about if you're serious about pursuing a PH build. Feel free to contact me with questions through my blog. I'd be glad to help if I can.