Welcome Lriley, 31 years? sounds like your in it for the long haul, I'm going on 36 with mine.. 
How much does it cost?...Just depends on how much you have to have it like new, can do yourself and of course how much the car needs. It would be easy to pay more than the worth to hire everything done. Interior work is actually some of the least expensive aspects from what I've seen.
cost all depends on your skills,,I had mine for about 27 yrs or so and started on it about 3 to 4 yrs back i think,,its in great shape now but far from finished,,did all work myself other than machine work and tranny rebuild but i rebuilt the motor to upholstering my own seats,,so far money wise i estimate $10 to $15k,,of course i added extras like a six pack and converted to a 4spd,,and cloned it to a 70 style as it is a 72,,so i spent more on making it what i wanted,,if i had left it stock , it proably would have cost me $10k or less,,of course i scoured ebay and other places for deals and could repair alot of things i bought that needed work,,of course if i count man hours i would be afraid to say what the cost would have been,,
