Hi Bobby,
I probably transfer your needs to mine too, so what I propose here is a little bit overkill ...
But if your professional pc builder guy is ok to deal with second hand parts (at least for the cpu), it might be possible to get an Intel system that will gives with much better perf for money ... (and still match your budget).
Pc cpu market is on hold since few years , so buying a second hand 4 years old intel cpu that was considered as high end at his time is probably the best move you can do.
Of course I'm talking about pure render performance for Terragen, for everyday tasks or gaming (GPU), an AMD system is doing fine.