Hey guys, whats the cost to build a good gaming rig these days??

I have the SH series (3, 4, and 5) and am using a Dell yadda yadda yadda lol but point is it barely runs Sh3, serious FPS issues when in harbours (I have GWX 3.0 and other mods enabled as well but even stock) and when ships are blowing up and such, but my friend can build me a gaming rig that could run crysis no problem and last time he said (over a year ago) it would be around $600 (thats about how much it cost him and his friend to build their own, 600 each) so my question for you all is how much now aday s would it cost to build a undeniably good gaming rig?? (good enough to run at least SH5 with NO fps drops in playability?? or at least moderate playability Im hoping for the $600 to $800 dollar range here