Lets say you get a job from a large company composed of smaller sister companies. One of their sister companie's websites has a shopping cart ready and everything. They want me to re-design and update a different sister companie's website (that doesnt support ecommerce).
If you know php but never programmed a shopping cart/checkout system before would you still programme it from scratch.. or use the other sister companie's shopping cart system or free shopping cart scripts available out there?
Also, how much would you charge them based on your answer from above? (This is a big company by the way)