When I got Directv back in August the offer was free hook-up for 4 rooms but I only got 3 rooms. So if I want to add a room now -how much would it cost?

hook up as in run coax cable to them or to activate a box? it's free to activate a box and only costs $5 per month for the service on that box. if you want someone to run coax cable, you are probably better finding someone local to do the job. if it's outside the existing house, probably $50 for an hour or two of work. if it's inside the attic, probably more.

A couple of years ago, we wanted to move one of our two receivers from upstairs to downstairs. Mind you, it had originally been downstairs, so all the actual work needed to put in a coax was already done. They were going to charge us $90, as I recall. We bought a long enough coax and I just moved the thing myself.

just go to Home Depot, buy the cable and other parts and do it yourself. not very hard

Doesn't it depend on what kind of dish he has as well? I don't know the details, but I thought certain dishes (or switches) can only have a certain number of boxes connected to it?