No hard facts from me...
I am not sure about prices, I assume universal.
Without observing it, trade sanctions should block trade between your empires. If you consider that you isolate an empire from the rest (you surround it, or they are behind you in a corner), you could make it very hard from them to get resources to build anything if you busted every mine of theirs in a previous war.
Blockades should work, but I have only seen its effect once (in Shadows beta, I think). It will at least prevents freighters from picking up resources (and I assume dropping off resources but I did not observe that). I watch a shipyard with a shortage ordering freighters to pick up goods at the blockaded spaceport next to it. Freighters headed there to fetch materials, but when approaching discovered the blockade and dropped the transport order. So the suffering shipyard had a shortage even if there were a ton of the required resources elsewhere. I do think ships went there to refuel, but it is a long time ago, and I was mostly amused at the stupid shipyard booking its resources from one that is blockaded. But if that was fixed, almost all blockades would be pointless.
If you blockade a capital you should mess up an empire quite badly, since it should be the default pickup point for resources for a lot of locations, and the transport orders will be booked to pick up and then be dropped.
I would guess you are correct, fuel cost is a balance between what you buy (refuel) from others and what others buy from you, or something. It is really hard to observe, I'd think.
I do not know, but this should be testable, if not a bit awkward to test. You know the cost of the designs (design screen). When privates do the first batch of orders in a pre-warp, you know what was ordered, you know the cost of their ships, and you can see the spaceport income you receive. This gives you the ratio between ship cost and your income. Since spaceport income can be quite significant, I'd bet 1 virtual caslon resource on you getting the ship cost.
It is a fee for using the spaceport, and for some reason they agree to base it on resource cost as a representation of complexity to build the ship...
< Message edited by Bingeling -- 4/21/2017 9:20:02 PM >