Though Apple products are ideal when it comes to graphics and other visual media, there are other great alternatives out there that won't break the bank.
You will need something with a lot of RAM (Random Access Memory) and a decent processor.
I recommend the Lenovo T430s. The Lenovo is an absolute beast of a laptop. I just rolled out about 2500+ of them to a very large beverage distributer here in the United States, and they are using these things for everything.
The reason this is a good choice is because you can load these things up with up to 16GB of RAM, which will be needed for rendering in AutoCAD. You can also get a docking station that is tailor made for this unit that has dual monitor capability - which I imagine you will need given the work that you do.
Lenovo has great support if you go for the warranty.