The VR helps me with my poor gunnery and lacking SA. You can get a VR and a card that will run it for prob 300 total.
Check out Rift S or Quest 2 on Ebay looks to be around 150.
For a video card I've done well with a 1070 looks to be under 100.
I used a I7 4770 for a long time too which you can get for a complete system:
Dell Optiplex 9020 Mini Tower Desktop PC, Intel Core i7-4770-3.4 GHz, 32GB Ram, 1TB (1000GB) SSD Drive, WiFi, DVD-RW, Windows 10 Pro (Renewed) $197
So I'm guessing you could get all the eye candy for around 500 if that helps.