Assuming you're talking US dollars, I expect you're looking at something like this...
basic case $40
~500W PSU 80+ Bronze $50
Windows 10 $90
mid-range B350 motherboard $75
8 GB RAM $90
256GB SSD $75
That's $420 before the CPU and GPU
So with an entry-level GPU (GTX 1050 - $125) and CPU (Ryzen 3 1200 - $110) you'd be at $655
You could go to a Ryzen 5 1600 (add $90) or a GTX 1050Ti (add $50). Both of these choices would offer some longevity for your system.
Personally, I am a big fan of used GPUs, since people are always upgrading and selling their old ones.