I know a lot of people are saying ~$1000 or more, but my system isn't even close to that and I run the newest STEP (plus even more) at 45-60fps. Mostly 1k textures outside and 2k inside, ENB (only a few things active), SweetFX, ugrids at 7. Â
I built my system myself for less than ~$600, including monitor. I see you aren't actually trying to build one, so I will spare the details. Â ;)