Cheapest sci fi basing around;
Old screen , glue on a base, cut edges off with scissors, glue on a model.
Cat-5 Cable, the wires inside, multiple colors as a bonus, twist some into a braid, coil some, pile some, glue on top of screen, cut off to the edge of the base after.
Nickles as a base are .05 cents each, NO TAX.
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Inexpensive Supplies
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Wire Hangers; from the dry-cleaners. I prefer the white plastic coated ones. (Cut-out the straight area and save). Then find a drill-bit the same size.
Uses; pinning large items, axles on vehicles, BANNER-POLES, etc… Alternatively, LARGE paper-clips.
Broom (Old); (house/kitchen) with long Nylon bristles. Depending on stiffness can be used as Spears, Lances, Antenna arrays, poles, cabling, and etc…
Stir-Sticks; wood, (NOT Popsicle, they are treated and can have a to-finished look). A handful from Starbucks for free with a cup-o-Joe or a box from a craft chain about $5.
Uses; as wood, for everything wood; floors, bridges, fences, and etc…
Cereal Box Cardboard; Save the front and back of the Cereal-box, etc. the cardboard is treated and very solid.
Uses, a VERY inexpensive substitute for plastic-card.
Rocks and Gravel; from your neighbor’s driveway (I Keed, I keed)
Uses; boulders, and etc…
Old Toys; from your closet, from a yard-sale, and etc.
Uses; rubble terrain, machinery, and etc…
Chopsticks; (fast food for free) Uses; large wood poles, fencing, supports, and etc…
Wrapping paper rolls; (the thicker ones) A Pringles can, oatmeal can, etc.
Telephone DSL Cat5 Cabling (inside wires); they have 4-12 different colored wires inside
Pennies (or nickels fit ROUND bases perfectly as weights; if you are rich
); (note; I have tried the washer and slug idea, trying to find the right size and driving around is not worth the penny, or the nickel) Alternatively, they could be cut in two (just off-center) to fit in the underside of the slotted-bases.
Roots of small hardy plants; use, dead (spooky) trees when turned upside down.
Hibachi skewers; (made of Bamboo) cost about $1 for a bag of 50 at local grocery store, great for spiky defenses, and etc…
Place-mat for dinner table; (made of Bamboo and other wood slat items) good for fences when cut.
Dykes; or heavy-duty wire cutters; NOT Sprue-Cutters (sprue-cutters are expensive and will get damaged when trying to cut metal or wood). Example;
http://www.xs11.com/forum/images/tips/20020902-floatpinremove.jpg Needle point embroidery colored thread; great for rope (28mm scale and up)
Fisk hooks, the tiny, triple ones, cut off sharp tips with dykes, make sure the eyelet is large enough to accept thread or wire; good for grappling hooks. Add a rope and litter the table with them, to represent places that can be climbed easily, cheaper than buying stairs, ladders, etc.