I'm in the middle of doing an overlay on our rental right now.

Single story, ~800 ft^2 on the main level (half basement room). One quote was $6500 for tear off and install. It went to $10k if they needed to put new sheathing on.

Soooo, I'm doing the overlay myself. laugh2

For the OP, I'd swag 5-10k, easy.

If you ever find yourself in a fair fight, your tactics suck.