maybe its just me but i dont understand your question entirely, if you are saying you wanna get High Definition reception on lets say 2500Rs external tv tuner then yes you can although i am not sure about the exact price but their are tv tuners which supports high resolutions as compared to the standard 480p reception in our standard TV. HOWEVER, you need to have HD source to by which i mean the cable operator must have HD broadcasting otherwise all your LCD and TV tuner will just be as simple card and CRT monitor.
Now lets talk about satellite. If you have satellite dish receiving HD channels and that dish is 1st connected to a receiver and then that receiver is connected to this external TV tuner box (as it called) then you can receive HD reception too. Alternatively there is a PCI DVB card available in all major cities for less than 4500Rs which requires no receiver and you can watch all the channels just like you watch on internal tv tuner card but the difference is that you will have satellite instead of cable/antenna.
There is no degradation in nice tv tuner card whether internal or external compared to standard TV reception and Remember you need to have a High Definition source to receive High Definition channels regardless of your equipment.
and you can check out this forum which is well dedicated to satellite and cable etc etc of Pakistan