You'll probably be looking to spend almost all of your budget on a CPU and Ram. The GPU won't really play any role in the rendering process with Strata.
Just choose a CPU that has as many cores at as fast a clock speed as you can fit in your budget. I dont have any experience with the new Ryzen CPUs from AMD, but I've been hearing good things, so I'd probably check those out... especially if you're looking so stay under $1000
A quick note...I seem to remember something about a 24 total core limit including virtual cores (12 multithreaded cores) in Strata 7.5... I might be crazy though... and I dont know if that would also apply to Strata 8. You'd have to look that up to confirm it. I just mention this in case you were thinking about going with the 16 core AMD Threadripper or something.