Keep in mind, the processor and screen size are things that you'll never be able to change; RAMand hard drive can always be upgraded later.
The Toshiba Satellite C665-P 5211 ( 24,500 approx) features a 15.6-inch screen, 4GB RAM and a 320GB HDD. The only downside is that it's powered by an older Intel Pentium Dual-Core processor. Still, this will be enough for office usage and web browsing, but high-end multimedia and gaming will suffer from poor performances.
AMD's APU Dual-Core processors have also proven to be credible performers, and the SamsungNP305U1A ( 23,900 approx) and the HP Compaq CQ43-405 AU (22,500 approx) seem like good prospects.
Samsung has the 500GB of hard drive space you're looking for, while HP will give you a larger 14-inch screen. The built-in Radeon graphics won't give you crystal-clear visuals, but it should handle multimedia and basic gaming well enough.