Oh wow ... a post for me.
Hmm.
Can you give me details of the space inside your car ?
Any brand you like in particular ?
A Kenwood dual pre subwoofer out deck should cost 6500-7000rs. KDC-MP439 for example.
Speakers ... JBL GT937e 4-5 thousand.
Subwoofer ... Kicker COMP 4ohm ... 7000 + box price
This subwoofer is nicely matched with your amplifier (unless you want something crappy like a 2500-3000rs kenwood/pioneer/xplod bs).
Kicker subwoofer will be bridged to the amp rear channels. Speakers to the front.
If you want components in the front instead of 6x9 inch speakers in the back then get JBL GTO series components for around 6500rs instead.
When getting a box made. Just tell the guy to make a box with 0.75 fibreboard of the size 18" width x 14" height x 12" depth (inches) ... AND MAKE SURE its sealed. No stupid holes or anything. Completely sealed box ... and dont listen to the box guy if he says bullshit like "Air nahe nikaligee awaaz nae aigee". Just tell him to make the darn thing ... theek ?