Ultrabook and dedicated GPU isn't something you're going to see often. Typically, you're going to be relegated to using a mobile workstation because ideally, for AutoCAD you're going to want either a Firepro or Quadro GPU which limits your options. Dell & HP both have good workstation options on the business side. I am partial to Dell's because they're typically cheaper but you'll have to do some customization to get exactly what you want. Replacing the system drive & memory is easy, but you'll want to pick the processor and GPU you need for your task and that is what will mess up your budget.
That being said, any high-end mobile GPU will get through CAD & Video Editting - if you don't need to purchase it right now, ASUS's GX500 is going to be perfect for you: thin and equipped with an 800-Series Nvidia GPU. No release date or pricing announced yet but that's what I personally am going to be getting once it launches.