For a USB 3.0 board you can also consider Gigabyte GA-785GMT-USB3 around 5.5k. So here is Cybertonic's config with slight modifications to fit in your budget:
AMD athlon II x4 635 - 5.2k
Gigabyte GA-785GMT-USB3 - 5.5k
RAM - 2 GB DDR3 1333 MHz from kingston/G.skill - 2.5k
Gfx Card - ATI Radeon HD 5670 512 MB - 5k
HDD - WD caviar blue 500GB - 2k
DVD Writer - Samsung/ LG - 1k
Cabinet - Zebronics Bijlli without PSU - 1.2k
PSU - FSP Saga 400W - 2.2k
Monitor - BenQ/AOC 20" - 6.2k
Keyboard + Mouse - Logitech combo - 0.7k
UPS - APC 550VA - 1.8k
Total - 33.3k
If you can squeeze in, go for 4GB RAM or just buy the RAM after a year when prices would have fallen further.
As said earlier, you won't need SATA 6.0 gbps as HDDs do not utilize even the available bandwidth under SATA 3.0 gbps. And as you don't want to upgrade for next 3 years, i hardly expect you to be buying an SSD in front of which, even gold looks cheap. Also the current technology of HDDs is not expected to yield much higher speeds as the technology doesn't offer much scope for improvement.