costs vary.
call hvac companies & get bids.

trane has another line called american standard.
same equip different name tag.
most brand names have another line also.

IMO install trumps brand.
load calc is for sizing equipment to meet needs
of house & occupants. rule of thumb sizing
usually results in oversized systems that cost
more upfront, more to operate & maintain.
mastic seal of all ductwork, plenum connections
& supply boxes should be required. not foil
tape, not duct tape. mastic.

discuss with hvac companies any comfort issues
you may ave. take time to get the right system
for your home.

best of luck.