Repairing or rebuilding a block wall
If an older wall has a few cracked blocks or tired mortar, a repair usually does the job and costs far less than starting over. If a retaining wall is leaning or has slid, the trouble is usually down in the footing or the steel, and patching the face won't reach it. Then rebuilding is usually the honest answer, because a new footing and new steel are what get the wall holding the soil again.
What sets the price of a block wall
The biggest cost is often below ground. A retaining wall needs a wider, deeper footing and more steel and grout than a freestanding garden wall of the same size, and a taller wall needs more of all three. Then come the site things. A steep yard means more digging and hauling, tight access slows the crew, a wall that steps down beside a driveway adds work, and a permit adds the application and an inspection. A surface coating or sealer adds to it too.