To estimate the range of HVAC costs, we used the following assumptions:

Total Home Heat Load (THL): 48,000 BTUs (4 Tons)

Electric Rate (ER): .000145/wH (Constant over 30 Years)

Annual Cooling Hours (ACH): 1700 (Industry DFW Area Estimate)

Average System Life (ASL): 7 to 30 Years

System Replacement Cost (SRC): $4400 (13 SEER) to $7400 (19 SEER)

Average Annual Repair Cost (ARC): $75 to $150

SEER Rating (SEER): 13 to 19

Efficiency Loss (EL): 0 to 40%

And the following equation:

Total HVAC Cost = (SRC x 30/ASL + ARC + THL x ACH x ER x (1 + EL)/SEER) x 30

Plug in the numbers and you get ~$28,000 minimum and ~$62,000 maximum. These number are approximations (they could be ±20%) and are two end points of a curve. Unfortunately, no research has been performed which helps estimate the shape of this curve. What is irrefutable is that your total costs can vary widely and depend primarily on your choice of contractor.