Several posts have been made about buying ships costing the full amount even if the ship has been partialy constructed.  I have noticed this and always thought it to be true.  While checking it out in a new game started with the Friday afternoon Opt-In (GalCiv3.exe version is 0.97.5), I found out that it isn't true, but it is a tool tip problem.

I had a partially constructed colony ship in a shipyard.  In the shipyard, the tooltip indicated it would take 1545 credits to buy the ship.  However, when the shipyard was selected in the galaxy screen, the tool tip at bottom-left of the screen showed it would take 814 credits to buy.  When I did buy it in the galaxy screen, my account decreased by 815 credits, which is within rounding error of the value expected from the tool tip in the galaxy screen.

After buying that ship, I started building another one.  After it had built for a while I checked the numbers again.
1905 credits to buy according to the shipyard tool tip.
 559 credits to buy according to the galaxy view tool tip.
I bought this one while in the shipyard.  My account was reduced by 559 credits, the amount shown in the galaxy view.

This means the cost of buying a ship is adjusted according to how far along the construction is, and the tool tip in the shipyard is wrong.