The cost of trademark surveillance depends on the same factors as any monitoring service: the number of jurisdictions, the channels covered, the frequency of reports, and the level of human analysis involved.
A basic register-only service for one jurisdiction is typically inexpensive. A comprehensive multi-country, multi-channel service with regular analyst-reviewed reports carries a higher cost. The appropriate level of investment generally scales with the commercial value of the trademark being protected and the number of markets where infringement risk exists.