What about labor? I'm pretty handy but there are definitely parts of my HVAC system where I'd be unable/unwilling to DIY it. I currently have a local HVAC contractor on-retainer for same-day emergency appointments - and honestly I don't think I'd be willing to consider anything less since my current heat pump is my exclusive source of heating in this house.
I'm in a temperate climate so there's little actual danger, but the idea of freezing/roasting my butt off for multiple days to wait for parts/labor is deeply unattractive.