At the end of the game, harvesters travel a lot of distance to collect rare materials for crafters in each cities via the market. For example, collecting from unspoiled nodes will make the harvester travel a lot more often to different areas, which are often far from each other and generate higher traveling costs.

Suggestion:
Popular harvester could build relationship (reputation) with the three main city, by providing materials to each harvester guild, and in exchange, have a reduced prices for teleports related to each city where the harvester is known and appreciated.

Example:
If a botanist helps a lot Gridania via the guild of botanists, the city, in exchange, will charge a lesser cost for teleports for all locations linked to it ( Black Shroud ).