Heatpumps can be put in for little or even no additional cost when replacing AC. I’ve done them for some of the lowest end projects as well.
The biggest deal is doing the correct calculations and picking the right equipment for the job. It’s 5th grade math but most people simply don’t take the time to do it.
Of course it’s definitely more idiot proof to slap in a 200% oversized gas heater and call it a day. You save a few hours of math but lose much more in equipment, materials and energy. For this reason many cities are now mandating engineering of any new HVAC