The machine for you is clearly the Mac Pro, since 8 cores aren’t enough, you could likely benefit from more than 32GB of RAM and you don’t want iMac Pro.
Even if there were a cut-down version for say $3k, would it even make sense to buy it? Compromising current capacities and capabilities—as well as future expandability—and for what? To save all of $50/month? (Closer to $35 after tax savings are considered.)
That makes little sense from a business perspective. Get the Mac Pro and you’re set. If you’re a working pro who needs/wants to run MacOS, it’s a no-brainer imo.