[Stormcrow]

You haven't found a definitive answer because there isn't one. The problem is that in the sources you cite, spaceships are treated like the economic equivalent of cargo vans. They don't cost millions or billions of dollars to buy, just thousands.

However, these costs are unrealistic, and rules like those in GURPS Spaceships don't handle them. You have to unrealistically force down the price of spaceships. If in a realistic, modern setting you could hand-wave average Wealth as including a heavily mortgaged house, in a cinematic space setting you can hand-wave average Wealth as including an old rust-bucket of a ship.