Quote: "buying the music from people that sell to anyone normally ends up badly, uncreative etc."
Well, it is a resource, and sometimes there can be good themes.
So, you can also dig the internet for music packs with all-purpose license (you can do whatever you want with the music once buyed):
I did some time ago a little google search with 'space music pack' and here are a couple of sites:
http://www.stockmusicsite.com/
"...purchase fully pre-cleared royalty free music tracks, loops and SoundPacks, then download instantly. Use the music from our library as many times as you wish in any type of audio-visual production without paying additional royalty fees. Perfect for films, tv shows, tv and radio commmercials, web sites, games, software, corporate use, embedded in products..."
Lots of songs, though it seems a little bit expensive.
Here is another one:
http://www.peaceloveproductions.com/index.htm
"These loops are royalty free in .wav .rx2 and .aif format"
They have some interesting theme packs at a reasonable price:
http://www.peaceloveproductions.com/Deep_Space_Music.html
http://www.peaceloveproductions.com/warpedspacepage.html
http://www.peaceloveproductions.com/uncharted_planets.html
Those packs have the single loops, not just the songs, intended to be able to compose your own songs with an audio editor & mixer software.
Just a quick search. I'm sure there are many other similar places and media around the web.