The proper connection of exterior walls to a floor system is a key component of a continuous load-path from the roof to the foundation. It will also make the walls less likely to detach from the house during an earthquake.
The following cost estimate assumes there is access to the sheathing on the exterior of the house and it is not being removed. Assuming that (40) straps must be installed in a house of typical size; the cost is approximately $200.
While the attachments are being improved, inspect the nailing pattern and weather resistant barrier to maximize performance and moisture resistance.