1st post so bare with me!
As far as handbrake problems go there are basically 3 options which i have experienced:
1. The front of the 3 cables snaps (from handbrake to the individual rear brake cables) which is my cars current condition!
2. 1 of the 2 rear cables, which go form the the front cable to each each rear wheel snap. (In my case, 1 snapped and the handbrake did not grip at all)
I would reccomend replacing both at the same time, as they have approx the same life expectancy and over their life will stretch. By replacing 1 will mean the old one is slightly longer than the new one = unequal force to each brake.
3. The handbrake assembly pulls up through the floor of the car (At the front of the handbrake). I fixed this myself with new bolts and some large washers to spread the force out (how it should have been made in the first place!)
I would do this DIY, no way would i pay for welding or whatever, mine is solid now.