You're looking for something like a 6600k/980ti platform:
PCPartPicker part list:
http://pcpartpicker.com/p/Cj67Lk
Price breakdown by merchant: http://pcpartpicker.com/p/Cj67Lk/by_merchant/
CPU: Intel Core i5-6600K 3.5GHz Quad-Core Processor ($259.99 @ B&H)
CPU Cooler: CRYORIG H7 49.0 CFM CPU Cooler ($34.50 @ Newegg)
Motherboard: Asus Z170-A ATX LGA1151 Motherboard ($153.99 @ SuperBiiz)
Memory: Kingston HyperX Fury Black 8GB (2 x 4GB) DDR4-2133 Memory ($56.99 @ Newegg)
Storage: Samsung 850 EVO-Series 250GB 2.5" Solid State Drive ($84.89 @ OutletPC)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($45.89 @ OutletPC)
Video Card: MSI GeForce GTX 980 Ti 6GB Video Card ($659.99 @ Amazon)
Case: NZXT H440 (Black/Red) ATX Mid Tower Case ($104.99 @ NCIX US)
Power Supply: EVGA 750W 80+ Gold Certified Fully-Modular ATX Power Supply ($90.99 @ NCIX US)
Total: $1492.22
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-10-20 23:53 EDT-0400
You could double the RAM, double the SSD, drop the HDD, double the HDD, get a cheaper case, get a more expensive case, get an i7 CPU, get a cheaper air cooler or a more expensive water cooler for the CPU, get a cheaper quality PSU, or get a haswell 4690k or 4790k and thereby save on the cpu, mobo and a little cheaper ddr3 but it wouldn't be as new of stuff, etc...for whatever way you want it, but that parts list I put there is about what you need for VR.
VR minimum req is the 970, but for the full experience at 90hz it looks like at least the 980 and probably the 980ti is you best best. The 980ti is way more GPU for the money than the 980 btw. The 980ti is also great for 2k. If you look at some benchmarks:
http://www.pcgamer.com/nvidia-geforce-gtx-980-ti-review/
you'll see that not even the mighty 980-ti can play ultra 4k at consistent playable framerates. For 4k you really would need 2x980ti's in SLI:
http://www.pcgamer.com/nvidia-gtx-980-ti-2-way-sli-nearly-doubles-performance-at-4k/
That's like $1,300 worth of GPU's though. Here's a potential build:
PCPartPicker part list:
http://pcpartpicker.com/p/Qv7cpg
Price breakdown by merchant: http://pcpartpicker.com/p/Qv7cpg/by_merchant/
CPU: Intel Core i7-6700K 4.0GHz Quad-Core Processor ($369.99 @ Newegg)
CPU Cooler: NZXT Kraken X61 106.1 CFM Liquid CPU Cooler ($119.99 @ B&H)
Motherboard: Asus MAXIMUS VIII HERO ATX LGA1151 Motherboard ($219.99 @ SuperBiiz)
Memory: Kingston HyperX Fury Black 16GB (2 x 8GB) DDR4-2133 Memory ($103.99 @ SuperBiiz)
Storage: Samsung 850 EVO-Series 500GB 2.5" Solid State Drive ($162.99 @ Newegg)
Storage: Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($66.89 @ OutletPC)
Video Card: MSI GeForce GTX 980 Ti 6GB Video Card (2-Way SLI) ($659.99 @ Amazon)
Video Card: MSI GeForce GTX 980 Ti 6GB Video Card (2-Way SLI) ($659.99 @ Amazon)
Case: Phanteks Enthoo Luxe ATX Full Tower Case ($142.99 @ NCIX US)
Power Supply: EVGA SuperNOVA 1000 P2 1000W 80+ Platinum Certified Fully-Modular ATX Power Supply ($184.99 @ NCIX US)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($17.89 @ OutletPC)
Operating System: Microsoft Windows 8.1 OEM (64-bit) ($87.98 @ OutletPC)
Total: $2787.67
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-10-21 00:09 EDT-0400