Obviously you will save money if you assemble a PC by yourself. It's pretty easy to do, actually. There is some risk that you will mess things up and short circuit components by putting them in wrong, which can be avoided by (a) reading up on how to do it and/or watching instructional YouTube videos, (b) being slow and careful in your assembly process.
The fact that you are not attempting to cram the kitchen sink in to your case will make it a rather straightforward process to assemble it yourself.
I've assembled about ten computers and nine were trouble-free; in the other I had to RMA (return to manufacturer) a part when it didn't work; I got the replacement in about three days. I find assembling PCs both fun and relaxing once you get the hang of it.
If you do build it (or even if you don't)... your parts list didn't include a power supply or floppy drive / CD drive / DVD drive / Blu-Ray drive. You will need the former and will probably want the latter. I suppose that you might be able to get away with using a USB flash drive or SD flash card for your I/O, but not all motherboards allow you to boot from them, so you might require a CD drive to load your OS. Some cases come with power supplies which can save you money. Your parts list doesn't include a monitor either.
I can't speak to the prices or suppliers in Kerala, but a good way of getting price baselines is to look on newegg.com, and find the USA tax-free costs. You can then gross those up to get a comparison price including import tax / VAT or whatever.
If you're looking to save money you might consider using a smaller hard drive. I'm not putting down the idea of a lot of storage, but given that you're creating a budget system, there is some savings potential there. You can also get a less highly rated CPU and overclock it to save money while getting the same or higher speed. Now, I'm a bit of an Intel fan (their high end stuff has been far superior to AMD's for the past five years or so), so it's a bit hard for me to say the following... perhaps you could get AMD stuff? On the low cost end AMD has better value so you could probably wind up with a faster and cheaper system going AMD (on top of the CPU cost, AMD-compatible motherboards are often cheaper).
You can save the cost of your graphics card if you get a motherboard with on-board graphics. However you won't have as good of a graphics subsystem; if playing PC games on your machine is a big interest, you may be frustrated if you go that route.
Since the rupee-US$ exchange rate is about 47 to 1, that rp15.000 budget is about $319. If you look in the New Builds section of this forum you could try to find something that fits your budget (remember to factor in taxes!)
Good luck!