Thats a pretty low price for an hvac system of that calibre with installation. I don't know what city you live in but that price wouldn't even get a second thought from contractors in my area especially me. I think you had better get a few more bids on the equipment from more experienced contractors, ones who will still be in business in a year from now. It looks like the Goodman Furnace is a 4 ton blower and the A/c unit is a three ton this may cause a problem with the cooling. I suggest you get three more bids from contractors with older license numbers.