Only Rd.100 more? No per channel charges? Also, later on, if I want a hd channel which is not part of my original pack, then I will have to subscribe to the sd and hd versions of the same channel, right? And pay both charges?
Yeah. If you want an HD channel for which you do not currently have the SD variant of, you will have to subscribe to said SD variant. You cannot subscribe to the HD channel, you can only get "access" to it when you have its SD counterpart.
tl;dr So, you will be paying "only" for the SD channels (not taking into account the audacious HD access fees).