I don't think it has to be that 'tricky'.The tricky thing is the range they can vary in.
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The Sidewinder pilot cannot afford to pay 10,000 credits per tonne for fuel. That would make the contents of their 2t fuel tank more valuable than their entire ship! (Thought they could refill in about 45 seconds with a 1E scoop, costing only 310 credits)
In your example, the sidewinder pilot just needs to check the map to find a 'cheap' system. The cost at extraction/boom could be 500cr a ton.
To be honest, I'm more interested in the 'flavor' this could add in the form of some dynamic missions and trading opportunities.