Okay, might be listed as a 'groundsheet' at this link but spent a bit of time yesterday having a look at an army surplus Individual Protection Kit
You can pick them up for about a fiver from a bunch of Army Surplus places, an the kit contains a 9' by 5' plastic tarp, 6 fairly light tubular alloy pegs and 50-odd foot of cord. Weight's not ultra-light (sub kilo, though) but the pack size when new is pretty small. Throw in a handful of tarp clips/clingons for ease of rigging and this could be an excellent budget starter into the world of tarping it.
One of the other links I've found only sells them in 4's, but they're only £4 a pop, so I reckon on stocking up. Even if they're more or less single use (which, from the feel of the nylon, they're not!) that's peanuts for a wee bit of shelter.
Cheap tarp option
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Cheap tarp option
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