Tyvek makes fine tarps. It is functionally waterproof AND it breathes enough that even with a tight, winter setup it will rarely form condensation.
In a pinch, Tyvek breathes well enough that you can wrap it around your sleeping bag to make an improvised bivy, altough I would allow for some ventillation just in case conditions favor condensation (in which case any bivy will have condensation inside).
Standard Tyvek 'House Wrap' weighs 2 oz per yard.
Tyvek glues easily with Barge's Cement or even Duco household contact cement as long as you rough up the area to be glued. It does not sew well because the stitch holes are like the perforations in paper - tear lines.
The strongest, lightest way to handle tie lines and stakeouts is to twist the corners and tie the lines on with a sheet bend.
A wonderful use of Tyvek is as a poncho/tarp. When softened, Tyvek feels almost like cotton, it has non-clinging body, and it breathes which adds up to the most comfortable poncho you can imagine. The hood or collar can be a simple rectangle on a slit instead of a hole. Then it won't pull out of shape when pulled longitudinally in a tarp setup. The collar or hood can then fold flat and not catch water.
New Tyvek is stiff and LOUD like a big sheet of aluminum foil. Soften it by wringing it or by running it through several cycles in a dryer with a pair of tennis shoes.
I don't know of any convenient source of Tyvek per foot. You might cruise building sites and talk to carpenters. I know folks who have bought it that way. A fair price is $1.00 per foot for 10 ft. wide Tyvek. Check the hardware stores. I have heard of smaller pieces being sold as drop cloths.