Here's a paper model of a chemical container train car I've used as a prop in my Savage Cyberworld -campaign. Print it on two A4/Letter sheets, on cardstock, 120g paper or something else strudier than standard paper. I haven't added instructions as the model is quite simple, and I didn't see it necessary to add the parts that attach train cars to each other (whatever they are called in English), model worked quite well without them.
If you want to create yourself cheap small-scale spaceships, you have two options available: Buy or find free papercraft starships, or scratchbuild them. This article shows you basics of scratchbuilding starships.
Materials and rules for scratchbuilding
1. Keep your eyes open; use anything, salvage things
Victory-class Star Destroyer is another vessel not seen in movies. It is predecessor of Imperial Star Destroyer, is 900 m long and has seen it's best years during the old republic. Although it's too slow to be too effective in ship-to-ship -combat, it still excels in one area: It is still the largest ship able to enter a planet's atmosphere. Combined with it's heavy weaponry, this attribute makes it excellent ground assault craft.
Did you assemble and paint WW2 military aircraft as a kid? I did, although I really didn't like much the glues and paints used in them, the ones I'm using currently in modelling and with miniatures are way easier to handle, an healthier too I guess. I also read Commando -comics and was generally fascinated about technology of The Great War. If you are also Plasticrack addict(tm), you'll be easily tempted to these.