Silly idea. A processor with enough cores + motherboard to support it and the multiple needed graphics cards will drive the cost past 3 basic computers.
This part list from a PCPP guide fits the bill:
PCPartPicker part list / Price breakdown by merchant
| Type | Item | Price |
|---|---|---|
| CPU | Intel Core i5-4690K 3.5GHz Quad-Core Processor | $219.99 @ NCIX US |
| CPU Cooler | Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler | $28.99 @ NCIX US |
| Motherboard | Gigabyte GA-Z97-HD3 ATX LGA1150 Motherboard | $94.99 @ SuperBiiz |
| Memory | *Team Elite 8GB (1 x 8GB) DDR3-1600 Memory | $47.99 @ Newegg |
| Storage | *Sandisk Solid State Drive 128GB 2.5" Solid State Drive | $49.99 @ NCIX US |
| Storage | *Hitachi Ultrastar 1TB 3.5" 7200RPM Internal Hard Drive | $42.00 @ Amazon |
| Video Card | *Gigabyte Radeon R9 290X 4GB Gaming Video Card | $299.99 @ Newegg |
| Case | BitFenix Comrade ATX Mid Tower Case | $56.99 @ SuperBiiz |
| Power Supply | EVGA SuperNOVA NEX 650W 80+ Gold Certified Fully-Modular ATX Power Supply | $78.99 @ SuperBiiz |
| Prices include shipping, taxes, rebates, and discounts | ||
| Total | $919.92 | |
| *Lowest price parts chosen from parametric criteria | ||
| Generated by PCPartPicker 2015-05-11 02:26 EDT-0400 |