Take two found-on-separate-occasions Shetland Wool sweaters. $5 and $6 at Goodwill.
Take them apart. Turn them into a blanket.
I edged it with Lion Brand Fisherman's Wool (in Oatmeal) to give it a more finished look, but it's otherwise a straightforward granny square with two strands of each colour yarn held together. If you're looking to make this, I suggest taking it slowly - each sweater took me a day to unravel, and Ravelry has me at about 22 days of making this between other projects.