Which mobile should i buy. My budget is under 6000 Rs

What the F U C K is Rs

If you are very strict about the 6000 budget your options would be Samsung Galaxy Star Pro S7262, Nokia Asha 502. Out of these the Samsung Galaxy Star Pro has better specs and reviews. I have limited the devices to these based on the brand so you don't have to struggle for after sales support. I suggest you read some reviews before you make a decision. To see the comparison, specifications and reviews check the sources below.

It nearly about $100, I'm looking for about the price of the mobile phone, found that several mobile phone for you
ThL V12 Android 4.0 Smart Phone MTK6575 1.0GHz 3G GPS 4.0 Inch IPS Screen $96.99 here: http://www.thlmobilestore.com/thl-v12-mtk6575-smart-phone-android-4-0-3g-1-0ghz-gps-4-0-inch-qhd-screen-white.html

DOOGEE DG120 Smartphone:
- 3.5 inch screen, 480 x 320 pixel display
- MTK6572, Cortex A7 dual core, 1.3GHz
- 256MB RAM, 512MB ROM
- 2.0MP rear camera, 1.3MP front camera
- Android 4.2
- $61.99
here: http://www.doogeemobile.com/doogee-dg120-smartphone-android-4-2-mtk6572w-dual-core-3-5-inch-2-0mp-camera-white.html

DOOGEE DG300 Smartphone:
- 5.0 inch screen, 960 x 540 pixel display
- MTK6572, Cortex A7 dual core, 1.3GHz
- 512MB RAM, 4GB ROM
- 5.0MP rear camera,2.0MP front camera
- Android 4.2
- $95.49
here: http://www.doogeemobile.com/doogee-dg300-smartphone-android-4-2-dual-core-5-0-inch-5-0mp-camera-black.html

Well converted to USD I think it will amount to around 100US Dollars

There are a lot of budget android phones for you to choose,
Your choice mostly depends on what kind of features/specs do you need in a phone. Like do you need a dual sim phone or something like that.

I would like to suggest these below phones according to your budget.

Sansui SA42G Mobile:-
a.) Dual sim support
b.) Android V4.2 jelly bean
c.) Processor 1 GHz
d.) 3.5 Inch screen size
e.) 256 MB + 512 MB internal memory

and, Micromax Bolt A37B Mobile:-

a.) Dual sim support
b.) Android v4.2 Jelly Bean
c.) Processor 1GHz
d.) 3.5 Inch screen size
e.) 256 MB internal memory

If you want a best deal on above Smart Phones, check Next.co.in or Flipkart.