The 2013 Mac Pro is an expensive system to assemble. It’s not just deciding which Mac Pro variant is best for a particular workflow, but also the type and capacity and speed and build quality and fault tolerance of external storage and backup. All of which can matter a great deal for some workflows.
The wrong choices can mean spending more money for less performance, inadequate storage capacity, confusing backup, or workflow configuration that does not utilize the best approach.
A complete system is not likely to come in under $6K even for the base model 4-core: a 4-core with with 512GB flash and 32GB and D500 GPUs is already $4199 and that’s before a display, AppleCare, external storage, backup drives, etc.
Professionals in particular might look at all these costs and wonder if they are making the right decision. For that I offer personalized consulting.