[Suicide Junkie]

You guys are all talking about the maintenance cost of the repair component, but the big expense is in maintaining your damaged ship.

If it takes only four turns to repair the ship, the cost to repair that ship is the same as the cost to build a whole NEW ship, and abandon the old one.

Every turn that you must spend on repairs costs you a lot of money in maintenance of the damaged ship, unless its mothballed at a planet.
Even then, it still costs you to unmothball the ship when repairs are finished.