Books are not the movie.
Ender got to another frontier planet in hours.
They have star drives.
If those ships were junkers, then inflation is a fat bastard, that $78 billion in new currency is 20 grand in old dollars.
From what we saw of the battle 20 years ago, Earth had conventional technology analogous with what we have in reality... All their space technology must have been adapted from the wreckage of the repelled fleet 20 years back....
Odd how they can reverse engineer all that from what what they found but ignore al the cultural data that must have been evident from the debris even if the drones were practically mindless.