Takara's "The Royal Museum of Science" is in my opinion one of the best miniature space models for quality and value. They are superbly built, all fully painted and just require some snap-together assembly. Each comes in a colourful box with a leaflet (in Japanese!), and sweets. Extremely sought after and difficult to find elsewhere.
There are three series: Series 1 Black, Series 2 Black and Series 2 White. All are £6 each or £15 for three. (including aircraft models - see "Aircraft" page.) Boxes are 'blind' ie you do not know which model you will get, which adds to the fun and makes them more collectable. To get your collection started you could buy one of each series. Or for £7 each you can choose a particular model while stocks last.

The Royal Museum of Science Series 2 Black: