Riptide has made a good point, but I'm thinking, we're using peacetime numbers.
Look at how much military hardware the allies turned out in world war 2. I can't speak for America, because I'm not american and don't really want to look it up, but I do know that by the end of the war, Canada had the 4th largest airforce and the third largest navy in the world (or it might have been the other way around). And that was unheard of for us at the start of the war, never mind now (1/12 of the population were active duty soldiers, with thousands more in service with the British forces). I have no idea how that lines up numbers wise with other countries, but I do know it was incredibly unusual for Canada.
Anyways, the point of that was this: In times of war, military spending in relation to the rest of possible uses for GDP goes drastically up, and it's not like the GTA/PVN beat the shivans, the shivans just.. disappeared. Unlike the Nazis, who were well and truly beaten, the shivans could return at any time, any place, without warning and obliterate us all.
The colossus cut-scene makes that much clear to be sure.
Mix in the neo-terran rebellion and I could easily see Riptide's estimate being a little bit shy, because the GTVA is either AT war, or pretty much has to act like it is, as the genocidal shivans could rear their ugly heads at any time.
And again, we just don't have any idea how densely populated, and how developed a system like say, Delta Serpentis, or Beta Aquilae would be. These places could be economic Juggernauts with populations in the billions.