Well we bought an older house, 55 yrs old. Want to replace all hardwood in the house. When I enlarged the closet upstairs I had to move a floor vent when I discovered the issue I will discuss. Now I have what I call "anti-ninja floors" they like to squeek upstairs no matter how soft you walk on it. I discovered that the floor was installed on the floor joists, NO SUB-FLOOR. So the crux of the matter...Do I put down moisture barrier, then lay the wood on top of it and nail it down? Or do I rip it all up one room at a time and install a sub-floor then proceed. The floor company wants 17K to do this, I think that is robbery. So I will leave what happens next to your advice.
Thank you for your time in responding, it is appreciated!

Personally I would rip everything up and install plywood then the new floor. I can't say for the price how many square feet?

its a huge job Chris ..except the fact.

your walls are built on top of your finished/structural floor.

it need to be ripped up which is hazardous..cut out at the walls..hauled downstairs and out.without falling through ceilings
work on top of joists to install new..get plywood upstairs.
glue/screw.

install new flooring..finish etc.
how big it is doesn't matter..rates vary.
this company gave you a price.

try a couple more.

you will probably hear its gonna be expensive or they just wont do it..easier ways to make money faster mentality or lack of proper skills.

you dont need to rip the existing flooring.
secure it where it squeaks..its a lack of fasteners causing this most likely.
over lay with 5/16-3/8 plywood.

install your new floor in preferred direction of choice.,