Definitely not worth it. Seeing as the 770~280X, you get something like this:
PCPartPicker part list / Price breakdown by merchant
| Type | Item | Price |
|---|---|---|
| CPU | Intel Core i5-4690K 3.5GHz Quad-Core Processor | $214.99 @ Amazon |
| Motherboard | MSI Z97 PC MATE ATX LGA1150 Motherboard | $88.99 @ SuperBiiz |
| Memory | G.Skill Ripjaws X Series 8GB (1 x 8GB) DDR3-1600 Memory | $48.99 @ Newegg |
| Storage | PNY CS1111 120GB 2.5" Solid State Drive | $55.99 @ Amazon |
| Storage | Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive | $48.45 @ OutletPC |
| Video Card | XFX Radeon R9 280X 3GB Double Dissipation Video Card | $219.99 @ Amazon |
| Case | Fractal Design Define R4 w/Window (Black Pearl) ATX Mid Tower Case | $89.99 @ Newegg |
| Power Supply | SeaSonic S12II 520W 80+ Bronze Certified ATX Power Supply | $58.99 @ SuperBiiz |
| Operating System | Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) | $86.88 @ OutletPC |
| Keyboard | Razer BlackWidow Wired Gaming Keyboard | $90.00 @ Mechanical Keyboards |
| Mouse | Razer DeathAdder Wired Optical Mouse | $41.98 @ Amazon |
| Prices include shipping, taxes, rebates, and discounts | ||
| Total | $1045.24 | |
| Generated by PCPartPicker 2015-05-09 03:41 EDT-0400 |
It includes everything brand spanking new for around the same price. You can skimp on components here/there and choose a build tailor made for yourself for far less than he's asking. To top it off, I know you're best buds 'n all but you don't know what condition his PC is in or how worn the components are.
When you're able to, always buy new.