I have been quoted 13K for installing a Carrier Infinity Central Air system 21 seer. Does this sound in line? Texas Gulf Coast area.

What's involved? Size of unit(s)? Any zones? 21 SEER is going to cost you.

2500 sq ft house... everything but.. most of the ducting was good as it was replace a few years back.. lines and all.

5 tons also sorry...

Just AC or AC and Heat. What BTU rating for the heater. What efficiency for the heater.
Better yet. Models of heat and AC units? Is Infinity stat included?