I am very much a DIY'er and doing my own HVAC repairs have never been out of the question. Actually, I have rebuilt a couple of systems, less the pressurized parts of the system.
HVACs are great until they aren't and the need for repairs always comes up at the worst possible time. It would be nice to know more details for those reasons.
If you ignore the direct question about charging an HVAC, there could actually be a small, slow leak in my system as it stands. That'll get troubleshot in due time. (Still, I don't think I have ever had a system that didn't need the system to be topped off after a few years, even with no detectable leaks...)
It doesn't seem difficult: Ensure system is at correct temperature; attach a gauge; depressurize/pressurize as needed.
There has to be some "gotchas" in there somewhere. The equipment is cheap enough and I am fairly sure I can source the correct refrigerant easy enough.
Aside from needing to store and manage a small supply of refrigerant and that there are some annoying risks (like a system freezing over, etc..), what cost factor and equipment am I not taking into account?
The refrigerant recovery machine is around $500 entry level, you also need the correct tank and a good scale. That's on top of the manifold, new refrigerant, vacuum pump, etc. I don't know much about it but I looked into it once upon a time for automotive DIY and decided it was too costly to mess with.