A buddy of mine just bought an oversized painting suit of what seems like the same material at Home Depot for about $10 and plans to rip the seams in the legs and glue them to together to make a mummy-shaped version. I'm not sure how that will work but it's a cheap, quick way to get a hold of some material.
This brings up something a bit off topic, but maybe worth exploring: Tyvek clothing for wind protection. I've got some Tyvek hooded jackets and pants that we used when working in a particularly greasy job (think Mike Rowe, Dirty Jobs). I need to get some of that stuff out and see what it weighs. I haven't priced any lately, so I don't know how it compares to nylon and polyester wind shirts and pants. I know that it won't be waterproof, so rain gear is out.
If it's not too heavy or pricey, it might be worth a look.