There is a section 'Navigators and Players' in the Shadow World Master Atlas Second Edition (p. 179) stating 1 gp/mile over land and 1 gp/10 miles by sea for each 'unit'. Additionally, costs for jumps are given.
Be aware that those prices were defined when RM worked under a gold economy hypothesis. Using a silver economy hypothesis, like RMU, would likely changed the prices.
I used those prices with a huge grain of salt. Basically, Navigator prices are out of reach of the common man, and that's that. If PCs use their services, they must be outrageously rich or have earned a significant favour from either the navigators themselves or someone who *is* rich.