What moves the price
Two homes can get very different prices for what sounds like the same job. The equipment is only part of it. The efficiency tier, the size of the system, changes to ductwork or venting, electrical work, permits, and how hard the old unit is to get out of the basement all end up in the number. Cost figures in these articles carry a date and a source, because prices move and a range from three years ago is not much help.
Cost of ownership
The purchase price is the number everyone looks at. Over fifteen years the number that matters is the cost of owning the system: what you pay up front, the energy it uses, what it costs to maintain, and the repairs you avoid while it is under warranty. A cheaper unit with a lower efficiency rating can end up costing more by the time it is replaced.
Plan before it breaks
Most replacements happen in a hurry, on the day a system gives out. If yours is getting on in years, pricing a replacement ahead of time gives you room to compare quotes, check incentives and choose the timing. The heating and cooling guides cover the warning signs worth watching.