Difficult choice: Recommendation for an Apple machine?

Some person requested me to setup or recommend a good Mac machine for 3D graphics. As of putting a lot of thinking for a few hours and still can’t go with a solution.

Graphics software will be mostly Autocad and perhaps some renderers.

As of seeing some prices the Mac Pro almost at 7000$ :expressionless: might be about 10% of an ideal choice here.

So going for a much more reasonable price, the iMac Corei5 seems a much more approachable at about 1500$-2000$. But still i5 CPU - 8 GB ram - Radeon/Intel GPU? Still I am in doubt about performance.

Have you ever used some type of 3D program in such machine? How about the RAM? I consider that 16 GB is mandatory in this case? Upgrading the ram is standard. Also what about the GPU? I consider that only with an external GPU PCI extension things can settle. And still I am not exactly satisfied with i5 but I can overlook it a bit.