I've ordered 2 Goodman systems off of the internet (eBay, Budget Air Supply). One a package heat pump, one a split system. Both brand new with warranty (although I haven't tested if it would be 5yrs or 10yrs)
I removed the old units, placed the new ones. I hooked up the duct work, and condensation drain. Electrical and thermostat wires were right there, read to go. Then I called an independant AC company. Paid an hourly rate. Split system was 5 hours. Package unit would have been ~3 hours, but I ended up hooking up the thermostat and wiring and had an AC tech look over the job and set the blower speed. Took less than 1 hour.
2.5 ton package system:
$1750 Goodman 14 SEER
$400 new elbow
$80 crane rental (unit was on the roof)
$30 Home Depot (tape, caulking, PVC pipe)
~$300 labor
2.5 ton split system
$1605 unit (condenser and air handler)
$40 Home Depot (Tape, Caulking, sheet metal, PVC)
$500 labor
$100 25lb of 410a
The package system is really easy, everything is together, charged and ready to go. Basically a huge window AC. The split system had a burned up the motor and lost all it's freon. But, if you still have pressure in the system, you will need to decide what you want to do. Legally you need someone to come and recover the r22. In my major city, there are people who will pay me to recover it, so it is a win. You may have similar options. For MANY years people just vented the freon and that was that. But, it is harmful to the ozone, so there's that... BTW, the same guy who put lead in gasoline, also created hcfc freon. Basically the wost things we did to the atmosphere, all from one guy...
So, after that, cut the refrigeration lines, unhook the wires, remove the condenser and place the new one. Do the same for the Air Handler. (Make sure to get the correct air handler, sideways/downflow/upflow) seal the duct work to the new unit.
It is a straight forward job, honestly.
I use Craigslist to find smaller companies and independent contractors/techs.
I've also had tons of success posting gig ads and detailing what I need done, and the qualifications needed. Then the phone rings and I find the exact people I'm looking for, ones that aren't busy and want to work....
Good luck!