That is a ridiculous extra cost. Maybe look at alternative systems

I'm wondering is that the additional controller or the builder's cost for making a change?

We're still in the planning phase and we can make addition. This is to add 1 wall mounted controller and Metricon charges $3.4k. The whole aircon system costs $17k. Crazy.

Sounds crazy. Maybe they know people will pay to avoid walking up and down the stairs . . and the seemingly reasonable overall price creeps up.

Hi , My house has very old twenty year old ducted air conditioning system . The wall system is downstairs and it was a pain turning it off . During a service , two years ago they discovered a remote inside one of the vents ! I now stand at the top of the stairs , aim and off it goes . Find out what model you are being given and google search if you can work your system from your phone . Perhaps the upgrade system will do so .