I've run into similar questions about cost of hiring someone, though for very different reasons. I don't have a table I use, or anything, but I usually look at the ballpark cost of an average meal and lodging as a starting point, then inflate above that by varying amounts based on the rarity or difficulty of the work they want to hire.
For example, if a meal is 1 sp and lodging is 5 sp (totally guessing here), then daily cost for just those in town is something like 8 sp. Weekly is maybe 40 sp (trimming for shopping in volume), monthly is maybe 160 sp or 150 if you like 50-tuples.
If the hireling is relatively unskilled, just go with this. For a profession that would involve apprenticeship and/or union and/or supervising, go to something like 250-300 sp/month. A position that requires materials (blacksmith, alchemist, tanner) would have added costs for their basic staples.
For a ship's captain, there's definitely wear and tear on the boat, and risk at sea, both of which would raise the cost of owning the boat and hiring them.