I was looking for this information myself but could not find it all at one place so I am going to list them all here for others who come looking for this information:
Airtel DTH SD Box : Rs 200 per month
Airtel DTH HD Box : Rs 250 per month
That was the monthly charge and if you want to buy the secondary box it would cost you Rs 1640 for SD box and for HD box it is Rs1800.
Videocon SD Box : Rs 200 per month
Videocon HD Box : Rs 225 per month
If you get one of the South silver or silver maxi packs with Videocon DTH then the second box rental is only Rs150 per month. They have a few more slabs too. Platinum south DH would cost you Rs250 per month for second TV.
SUN Direct DTH :
It was not very clear but from what I understand you get a Rs200 discount for the second box rental so for example if your subscription charges ar 500Rs per month and you get a second box for another TV then your secondary box rental would be Rs300? That is what I understand. Please correct me if I am wrong.
Tata Sky DTH :
Tata Sky multi tv subscription charges : Rs200 per month
I will add the rest later on