There is a way to buy items that costs more than 2.5 bills.
As you know, carrying credit cards on board allows you to break the 2.5bill credits limit. So, when you are going to buy something that might cost like 6 billions, just carry 1.9bill as credits, and the rest as credit cards. You transfer them to the seller during the ship buying process.
I still don't know if a single ship can cost more than 2.5 billion credits tough..
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CS whoring is something that, as an Asgard, I had to face quite often.
The last 5 wars were against CS fleets. We used fighters, and bombers, as some occasional CS too, and even outnumbered and out gunned we won them all.
That is because people think that a battleship, with all its raw armor and firepower, can pwn anything on their path. That seems logical, but said people forgot that all BS have an accuracy problem which is related to the target algorithm used by FL.
FL targeting algorithm was meant for fighters, where all weapons are very close to each other, so the cross air is in the average center relative to all active weapons (and the time taken by the bolts to travel the length of the ship is neglected, because it almost inexistent). But, with a battleship, where some guns are 1-2k away from each other, the algorithm fails because the time a shot takes to travel the length of the ship is not computed. So the shots arrive to the target out of phase...
The only way we have to solve that is to make the muzzle velocity very high, in the range of 5-10 k/s. That way, the time taken by a projectile to travel the length of the ship is much smaller, and the accuracy bug is diminished to an extent.
The true way to solve it would be to rewrite the targeting and firing algorithms to make them fire the guns on a sequence (i.e: the furthest weapons to the target fire first, then when the bolts reach the position of the closest guns, the closest ones begins firing), but as we don't have FL source and that is hard coded into the game itself, it's not possible to solve the problem that way.
(If you find any mistake in my English, please let me know via a PM)
(Really, I speak terrible English, so please, tell me if I make mistakes. I'd like to improve it a bit )