Just to compare-a 40,000 BTU water source heat pump us about 4.3-5000.00 bucks give or take. The unit takes about 4 hours to install.
Produces heat/cold and will produce all the hot water you need in the house by a super-deheating exchange coil. And, this unit uses less electricity than a normal DX HVAC ..... supposedly.
I have never been sold on ERV units for residential mostly, because the performance claims all these units. Both performance specs the ERV and WSHP have are lab setting testing.
Yes, most are for perfect conditions and as I am not in Hawaii , I don't live in perfect.
THE smaller cross-flow, like the Trane, are roughly 50% efficient. The larger linear flow can be as much as 80% as they have far more surface area. There are some objective tests out there.
I have a gas tankless DHW and a high efficiency gas furnace. Most of my electric bill goes to the mini-split in my workshop.
When building new, you can do clever things like drop a ground loop in the septic trench for a low cost geo-thermal. A friend has a large lake, so he tossed a 500 foot roll of plastic in the bottom of it. Lots of smart things to do if you can. Expensive for older house.
My main concern is air quality. Reasonably tight house, but two dogs and who knows what else. Goal is for fresher air, not super efficiency.
I was looking into solar as I have a perfect roof for it, but in NC, it is rigged where you have to buy it all yourself. Payback is about 35 years on a system with a 10 year life span. In MD, you could lease your roof. No cost, and got about 2/3 of the electricity cost back. No maintenance.