You have no idea how much high performance 2 stage polyurethanes cost. High performance polyurethane top coats for flooring go for $120 a gallon which include 1 quart of hardener. 1 gallon of hardener alone costs nearly $200. Go lookup what PPG sells these things for. The difference between a $300 dollar paint job and a $5000 dollar paint job is mainly the materials. Automotive grade polyurethane sells for $250+ a gallon and can require as much as 2-3 gallons for a nice paint job. That doesn't include the primer and base coat. You're looking at $1500 dollars for materials for a high quality paint job. And if you're looking to do a complete color change on a stripped car...double that price in materials.