Because it is hypothetical I decided to list the realistic specs that a CAD workstation would be built around these days. When talking about theoretical specs for a system in college work then you should really be looking at the current real world specs, rather than something that can just about run the application that in the real world would be impractical.
For budget the realistic minimum has to be £2000, although for a home based CAD designer or university student you could build a PC for around £1000 including monitor that would run AutoCAD at a reasonable speed.