That's because you're a fence sitter Wally.

Imo the amount of stuff the station will buy is too low. 800-1000 units or so in the station and the buy price tanks. Conversely when there is few items like less than 400 the price skyrockets. This high pricing is what is causing the trade guild missions stuff to be super expensive. It is just a symptom of the too low station stock amount. The whole thing flops so fast with so few items that trading with the station is pointless.
Also I think there should be some kind of NPC demand for stuff from the stations. Like a random check every 15 mins with a chance that some number of items will be gone from the station do to NPC demand.
Still exciting I think the potential is there. Please don't make all the stations like N2 until we get it a little better though. About all I do in game is trade and I would be sad if stations did not want to give me profit for hauling stuff.