building faster?

[Merry Jolkar]

What is the rule for determining the cost of a refit? I'm trying to retrofit, and have more than twice the resources required by the target upgrade ship *brand new*, but keep getting message that I don't have enough. Any help would be appreciated, as this is a critical part of my strategy and I've been stuck for 3 turns now!

I have
169,109 minerals
16,802 organics
118,376 radioactives.

and when trying to retrofit a ship that costs
76,000 minerals
1000 organics
32,000 radioactives
brand new, I get a message: "Our vehicle Gate 1 in system Texrek has not been retrofit, sire. You do not have enough resources to finance this retrofit."

I have more than twice the value of the ship, *and* I'm retrofitting from a ship that costs:
54,000 minerals
5000 organics
13,000 radioactives. (Note that the initial ship seems slightly less than 2/3 the value of the target but I think this is due to rounding.)
Thanks,
Merry