One thing I just realized is that much of the discussion about the cost and profit of cargo is concerned around speculative trading. Buying x here, and selling it someplace else to make a profit. While this is all good and all, much of the trade deals are going to be done by parties that just need someone to deliver the cargo - often this will be the PC's just trying to make some money. Having worked in a warehouse I see it all the time, the truck shows up, says I'm here to pick up 7 skids, somebody loads it gives the driver the paper work and they head out.
So, a party could make money to pay their way with doing jobs like this. In fact, these will be the common guaranteed jobs (not including plot twists such as illegal goods and pirates). It takes a certain type of person to do speculative trading, and not every group is going to want to do that. It is something that should be factored into the trade.
Now, as to the cost of landing fees and such, perhaps something as simple as 50 credits per silhouette? Use this as a base, some places will charge more, some less. Each success on certain checks could reduce this by 10-25 credits, and a Triumph by 50-100? Threat and despair being the opposite.
I think if the costs were based on the silhouette, both docking and recharging it is basic enough to cover most situations.
As much as I do like Traveller, I feel Star Wars isn't the right place to be constantly trying to buy low and sell high just to make ends meet. This is just my perspective though, and if you have fun selling Taun-Taun sleeping bags to campers on Endor, then by all means play that way. But it's not the spirit of Star Wars.
You're going to find that many of the truths we cling to depend greatly on our own point of EU.