If you want to move to DTH then Tata Sky will be best choice because of it's better Services, complete transparency in charges and best customer care.
If you purchase new connection from local dealer then you may also get 6 months free subscription. There is 0 day lock in period and Channels/packs can be changed through website, app or local dealer anytime you want.
Charges will be deducted on daily basis which means if you subscribe for Rs. 22 Channel then 22/30 = 0.73 per day. After TRAI rules everyone is equal in terms of Cost, so your monthly charges will depend totally on your subscription.
Online price of new Tata Sky without any Subscription :
SD Box - Rs. 1399
HD Box - Rs. 1499