Star Trek Legacy

Once you've beaten the last mission, been through the the credits, save your progress, & then go to the main menu.
On completion of the last mission, save/continue so it takes you back to the title screen through the credits.
Choose to continue campaign, which replays the last mission, when you beat it again, save & back to the main menu - Doing this your command points will build up. Keep going through this til you can afford the extra 3 Sovereign class, as the 4th ship will be the USS Legacy

choosin to replay the mission from the mission complete screen get's you nowhere - doing this I always had the 3k I finish with when it came back to the fleet screen, not the 6-7k I had at the end of replaying the mission

I actually got the mission done quicker with 3 of the best cruisers (nebula have 4 forward, 3 aft torpedo launchers, with a good lock-on, useful against cubes) The sovereign class are slow to get a lock-on (and only 3 forward & aft). The extra speed of Nebula & Intrepid was far more useful in this mission, I waited until I had the command points to buy all 3 in one go

It's 57,000 command points for 3 Sovereigns.

Keep replaying the very last mission until you have enough Command Points to buy 3 Sovereign class ships (you'll then have 4, including the Enterprise). The last Sovereign class ship you buy will be the U.S.S. Legacy.

(How lame!)