re: What is a reasonable quote for a new AC unit for 1800 sq ft house?

I don’t know anything about Daikin brand, but is it 3.5 ton downstairs and 3.5 ton upstairs?

I don’t think either sounds high if they are the total price for two 3.5 ton systems installed (again don’t know anything about Daikin), but You might not need 3.5 tons on each floor.

Edit: I misread post, missed the duel zone system part, and focused on a duel unit system.