I can only speculate, but in my last replacement scenario, higher-SEER units (17+) had dramatically higher quotes, to the point where it was difficult to justify financially. On top of that, there were dramatic (~100%) variations in prices on similar equipment (but different brands) between installers. I can only imagine that regional differences are yet another source of variation...
All that is to say, my first guess is that the GP was quoted a high-SEER unit for name-ish brand equipment.
All that is to say, my first guess is that the GP was quoted a high-SEER unit for name-ish brand equipment.