Sample:

Intel i3-2100 + H61 board (used) - P4,000
Sapphire HD 7770 video card (used) - P3,500
Corsair VS450 PSU (bnew) - P1,650

Total: P9,150

Just recycle your old case, hard drive, disk drive, and peripherals (keyboard, mouse, etc). I recommend a brand new true-rated PSU because too many idiots use generic PSUs then wonder why their PCs conk out too early on. Generic PSUs (like what most PC bundles are sold with) give erratic current/voltage which can damage your components and cause them to fail prematurely. They are also less efficient (nowhere near 80% efficient which is the industry minimum).