Hey guys , anyone know the max range of avionic rcb6i (rc bazzar one) , and is there anyway the range can be extended to 3-4 kms ??

As per this video the range went up to 1.2 kms. Generally for long range flying, a lower frequency module such as 433 MHz is used with a transmitter such as the Turnigy 9x. I am not sure how you can (legally) increase the range of the RCB6i since I think there are regulations on max transmission power.

Yeah i saw that video , but can i use a polarized antenna or something 2 increase the range??

I don't really know much about radio theory so I am not the best person to help you. I just did some reading and from what I saw, circular polarised antennae are generally used for FPV. According to this web page http://blog.oscarliang.net/linear-circular-polarized-antenna-fpv/ , linear antennae actually have better range. Polarised antennae are used mainly because they reduce multipath interference (when the radio waves bounce off objects) since circular waves will just change their polarisation when they strike objects. The problem is that if left-hand polarised waves are received by right-hand polarised antennae (or vice-versa), there is a 30 dB power loss. I think it is best to use a transmitter with a long range module such as the EzUHF The website sums it up like this:

When to use circular polarization:

your receiver is close to large obstacles such as trees, or buildings (within 30meters)
acrobatic flying (constantly changing the position of the plane)
low altitude flying
flying very high altitude (you need a directional antenna)

When to use linear polarization:
flying out in the open field with no obstacles
very stable fly, does not roll or pitch a lot
long distance flying
standing on top of a hill
have no space for large antenna

How much will a long range module cost me ? , any stores in India?

You will need a transmitter with interchangeable modules such as this http://www.edallhobby.com/en/turnigy-24ghz-transmittersreceivers/498-turnigy-9xr-transmitter-mode-2-no-module.html (Rs. 6500) or this http://rcmumbai.com/index.php/product/turnigy-9xr-pro-radio-transmitter-mode-2-without-module/ (Rs. 8800). You will then need a UHF module such as this http://rcmumbai.com/index.php/product/ezuhf-433mhz-direct-fit-jr-module-for-the-9xr-and-taranis-uhf/ (Rs. 7000) with a receiver like this http://www.rcproduct.in/uhf-lrs/111-immersionrc-ezuhf-8-channel-diversity-receiver.html (Rs. 7500). As you can see, it is very expensive. A cheaper option would be to use the transmitter I mentioned with the OrangeRx module and Rx: http://www.rcproduct.in/combo-offers/50-open-lrs-433mhz-transmitter-1w-open-lrs-433mhz-9ch-receiver.html (Rs.4349- out of stock). This needs quite a bit of setup and programming skill.

I am not sure about the legal issues surrounding the use of these frequency bands. Also, you have listed your RC skills as Beginner. The equipment I have listed is a very powerful, long range system for experienced FPV pilots. I suggest you do some research and decide on whether you really need this level of equipment and have the skills necessary to manage flying like this.

I don't have any direct experience of this, I am just suggesting things based on my research. I request more experienced members to comment on the setup I mentioned.

Actually there was a guy who mentioned in d review of avionic rcb6i , that the range of it can be extended to 4kms by increasing the antenna gain , so I had this doubt abt d range ...

Increasing the antenna gain will give you greatly improved range in some directions but a drastic drop in other directions. You would find it harder to keep the antenna oriented right as the gain is increased. Again, I don't know about the legal issues surrounding this.