Thats actually not a horrible budget. I think mine was only 1000 or so. Honestly been awhile since I looked at this kind of stuff seriously but umm, given your conditions, this is what I came up with (https://pcpartpicker.com/list/JhCPHh)
Honestly, for the storage I'd actually just use the old storage from your current system, which saves about 100 dollars. I'm also assuming you don't need a new OS or peripherals. Tried to prioritize CPU over everything else, since main purpose is KSP. Graphics card should be decent enough for most things.
Not sure though if its exactly your best bet because i tried as best as possible to color coordinate, not look purely at price to performance, but I'd say it's a start.
I also realize its not the exact case you showed but uhh... its what they had on that site.