taking off the gearbox and fitting it in is a time consuming task, 6k is reasonable rates given that its karachi, towards the north, it would probably drop to max 3k, but not more.
If its labour you are worried about, try to find more inexperienced people and the labor amount will decrease.
I just got the torque converter seal of my pajero replaced yesterday.
I took a market survey, got quotations from 6k to 30k Rs., I had decided to go with the 15k one but that fellow kept on delaying and giving excuses, in the end settled for the 12k fellow, it took 2 hours to dismantle, 4 hours to get all the parts and 2 hours to put back together.
so opening and closing is 4 hours, but finding the parts, and making sure that there isn't any leakage and doing it right, takes time, 6k labor for karachi in a time where milk is 140/litre, seems reasonable