If you want to increase tour budget to 30K then I think you can go with Pheom II quad cores to cut some budget. It is marginally better than COre i5 processors and far better than Core i3s. This config is with revised price also.
Phenom II X4 945 (3 GHz quad core with 6 MB L3 cache, 95W) @ 6.1K
Asus M4A78LT-M LE @ 2.6k
Kingston 2X2 GB 1333 MHz DDR3 @ 2.6K
Seagate 500 GB 7200.12 @ 1.7K
LG 22X SATA DVD @ 0.9k
Gigabyte LC400 80+ @ 1.6k
Normal Zebronics cabinet without SMPS @0.8K
Zotac 9600 GT eco 512 MB GDDR3 @ 3.6K
Logitech Keyboard + Mouse combo @ 0.5k
A.O.C 19" LCD (1440X900) @ 5.5K
APC 600VA UPS @ 2k
Total 25.2K...within your budget.
reason:
1. Processor: The kind of applications you've mentioned are heavily multithreaded and can take advantage of 4 physical cores n better than 4 logical cores of i3/i5. The new 945 is of 95W, check before purchasing
2. Motherboard: As you are not gonna overclock, you simply don't need a 8+1 pin or high end mobo. This mobo is based on AMD 760G chipset and should be fine. If you want something better, go for MSI 785GM P45 @ 3.6K
3. Replaced Dell with cheaper 19" LCD. It is very good monitor. My friend is using for 2.4 Years and it is really good. you will also have one resolution over 18.5" monitors 1366X768
4. Added a low end nVidia card. Reason is the kinda applications you're working on supports nVidia CUDA and will be highly benefited from a nVidia CUDA enabled graphics card due to GPU assisted processing.